Acids, Bases and Salts
Ques.1 What are acids and bases?
- Solution that produce hydrogen ions and turn blue litmus are red called acids.
- Solution that produce hydroxide ions and turn red litmus blue are called bases.
Ques.2 What are the physical properties of acids and bases?
Ans.2 (a) Acids- most acids are colourless. They are sour in taste.
- Acids are very corrosive in nature. they can burn skin an clothes.
- Acids produces H+ ions in solution form.
- They turn blue litmus red.
(b) Bases- Bases are colourless. They are better in taste.
- Bases are soapy to touch.
- Bases produce OH– ions in solution.
- They turn red litmus blue.
Ques.3 You have three test tubes. One of them contains distilled water and the other two contains acids solution & a basic solution. If we have only red litmus, how will you identify?
Ans.3 the solution i.e acidic does not change the colour. Basic solution change red litmus blue.
Ques.4 Name a few acids and bases?
Ans. 4 Acids
- Hydrochloric acid (HCL)
- Sulphuric acids (H2So4)
- Nitric acids (HNo3)
- Ethanoic acid (CH3COOH)
- Sodium hydroxide ( NaOH)
- Potassium hydroxide (KOH)
- Calcium Hydroxide (Ca(OH)2)
- Magnesium hydroxide (Mg(OH)2
Ques. 5 Give the colour change of acids and bases with following indicators.
|Sample solution||Red litmus solution||Blue litmus solution||Phenolphthalein||Methyl orange|
|Acids||No change||Turns red||No change||Red|
|Bases||Turns blue||No change||Dark pink||Yellow|
Ques.6 What are olfactory indicators?
Ans.6 Same substances change their odour on treating with acid and bases. These substances are called olfactory indicators like onion, vanilla, cloves.
Ques.7 How do acids react with metals? Give reactions.
Ans.7 They react with metals in the following way
Acids + metals → Metal salt + Hydrogen gas
2HCL +2Na → 2Nacl +H2
2HCL + 2K → 2KCL + H2
2HCL + 2Zn → 2ZnCl2 +H2
2HCL + Ca → CaCl2 +H2
2HCL +Mg → Mgcl2 + H2
2HCL +Fe → FeCl2 + H2
6HCL +2AL → 2ALCL3 + 3H2
H2So4 + Zn → Zn So4 + H2
H2So4 + Mg → MgSo4 +H 2
H2So4 +Fe → FeSo4+ H2
Ques.8 How does zinc react with sodium hydroxide?
Ans8. When zinc is heated with sodium hydroxide sodium zincate is formed and hydrogen gas is liberated.
2NaOH + Zn → Na2ZnO2 +H2
Ques.9 How do acids react with metal carbonates and metal hydrogen carbonates?
Ans. Na2 Co3 + 2HCL +Co2 + H2O
NaHCo3 +HCL → NaCl +Co2 + H2O
Metal carbonate/ hydrogen carbonate + Acids → salt +Co2 + water.
Ques 10 What happens when Co2 is passed through lime water? What happen when excess Co2 is passed through lime water?
Ans.10 Ca(OH)2 +Co2 → CaCo3 + H2O(white ppt)
When Co2 gas is passed through lime water,it turns milky due to the formation of an insoluble white ppt of CaCo3.
If we pass excess of Co2 through the mixture, the white ppt will vanish due to formation of soluble calcium hydrogen carbonate.
CaCo3 +H2O +Co2 → Ca(HCO3)2
Ques.11 How do acids and bases react with each other?
Ans.11 when an acids react with a bases, salt & water are formed.
Acid+Base → Salt + water.
HCL +NaOH → NaCl + H2O
H2 So4 + 2NaOH → Na2So4 + 2H2O
HCL + NH4OH → NH4CL +H2O
H2So4 +Ca(OH)2 → Ca So4 +2H2O
Ques.12 How do acids react with metal oxides?
Ans.12 When acids react with metal oxides which are basic, they from salt and water .
Acids +Metal oxide → Salt + water
Na2O +2HCl → 2Nal +H2O
MgO +2 HCl → Mgcl + H2O
Ques.13 How do non-metal oxide react with bases?
Ans.13 Co2 + 2NaOH → Na2CO3 + H 2O
So2 +2 NaOH → Na2 SO3 + H2O
When non-metal oxides react with bases they form salt and water.
Ques.14 Why should curd and sour substances should not be kept in brass and copper vessels?
Ans.14 This is because the metal will react with the acids in the food.
Ques.15 Which gas is usually liberated when an acid react with a metal? How will you the presence of this gas?
Ans .15 Hydrogen gas .
We will test it by brining burning matchsticks, if it produces pop sound, then hydrogen gas is liberated.
Ques.16 Why do acids conduct electricity while glucose and alcoholic solution does not conduct electricity?
Ans.16 Acids conduct electricity because they produce H + ions in solution while glucose and alcohol solutions do not conduct electricity as they do not produce H+ ions in them.
Ques.17 Why does dry HCl gas not change the colour of dry litmus paper?(reference activity.2.9)
Ans.17 It does not change the colour of dry litmus paper as H+ ions are not produced in dry conditions. So HCl gas will not change the colour of litmus. But if we take wet litmus then its colour would change as the dry gas will produce ions in water of paper.
Ques.18 What happens when acids and bases are dissolved in water?
Ans.18 When acids dissolved in water, they split up into ions and H+ combines with the water molecules to form H3O+ ion.
H2O + HCl → H3O+ + Cl–
When bases are dissolved in water, they form the positive metal ion and the negative hydroxide ion.
NaOH — H2o—> Na+ + OH –
Ques .19 What are alkalies? Give example.
Ans.19 Bases that are soluble in water are alkalies e.g KoH, NaOH, Ca(OH)2.
Ques.20 While diluting an acid, why is it recommended that the acid should be added to water not water to acid?
Ans.20 The process of dissolving an acid or bases in water is highly exothermic process. The acid must always be added slowly to water by constant stirring. Water should never be added to concentrated acid as the heat generated may cause the mixture to splash out and cause burns, the glass container may also break due to excessive local heating.
Ques.21 How is the concentration of hydronium ion affected when a solution of an acid is diluted?
Ans.21 Mixing an acid or bases with water results in decrease in the concentrations of ions ( H3o+/OH–) per unit volume. Such a process is called dilution and acid or bases is said to be diluted.
Ques.22 How is the concentration of hydroxide ions affected when excess of base is dissolved in solution of NaOH?
Ans.22 When excess base is added to a solution of NaOH, the concentration of hydroxide ions will increases per unit volume and in the whole solution also.
Ques.23 With the help of a figure show the variation of ppt with the change in concentration of H+ and OH– ions?
Ques.24 You have two solutions , A and B . The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which one is basic?
Ans. 24 Solution A has more H+ ion concentration . A is acidic & B is basic.
Ques.25 What effect does the concentration of H + ions have on the nature of solution?
Ans. When the H+ ion concentration is more than the OH– ions, the solution is acidic.
When the H+ concentration is equal to OH– the solution is neutral .
When the H+ concentration is less than OH– the solution is basic.
Ques.26 Do basic Solution also have H+ ions ? if yes then why are they basic?
Ans.26 Yes, basic solution also have H+ ions yet they are basic because H+ concentration is less to OH– ions.
Ques.27 Under what soil condition do you think a farmer would treat the soil of fields with quick time or slaked lime or chalk?
Ans.27 The farmer will treat the soil in his field with quick lime (Calcium Oxide) or Slaked Lime if soil becomes acidic. Testing the soil with these materials will neutralize the soil and make it fit for crop cultivation.
Ques.28 Write a short note on importance of pH in everyday life?
- pH in our digestive system: Our stomach produce Hydrochloric Acid which help in digestion of food without harming the stomach. During indigestion, the stomach produce too much acid and this causes pain and irritation. People use bases to get rid of pain.
- pH changes as the cause of tooth decay: Tooth decay starts when the pH of mouth is lower than 5.5 . Tooth enamel, made up of Calcium Phosphate is the hardest substance in the body.
- Self defence by animals through chemical welfare: Bee sting leaves an acid which causes pain and irritation. Use of mild base on the sting area gives relief.
Ques.29 What are salts? How are they formed?
Ans.29 Salts are the combination of positive metal ion and negative non- metallic ion or poly ions.
They are formed by neutralization reaction of an acid and a base.
e.g NaCl, MgSo4 etc.
Ques.30 Give the formula for following salts?
|Salts||Formula||Acid||Base||Type of salt|
Ques.31 Name some families of salt ?
Ans.31 Salt belongings to same group of positive & negative ions form one family. E.g Sulphate family (K2SO4, MgSO4)
, sodium family (NaCl, NaNO3)
Ques.32 From activity 2.14 get the formula and type of salt?
|Copper Sulphate (acidic)||CuSO4||H2SO4||Cu(OH)2||2-3|
|Sodium Acetate (Basic)||CH3COONa||CH3COOH||NaOH||10 above|
|Sodium hydrogen carbonate||NaHCO3||H2Co3||NaOH||10+|
Ques.33 Why does distilled water do not conduct electricity while rain water does?
Ans.33 Distilled water is a pure form of water, it does not have any ions in it, so it does not conduct electricity while rainwater has ions in it, so it conducts electricity.
Ques.34 Why do acids does not show acidic behaviours with absence of water?
Ans.34 This is because no ions are formed in the absence of water.
Ques.35 Five solutions A,B,C,D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9. Which solution is neutral, strongly alkaline, strongly acidic, weakly acidic, weakly alkaline?
Strongly Alkaline: 1(B)
Strongly Acidic: 11(C)
Weakly Acidic: 4(A)
Weakly Alkaline: 9 (E)
pH in increasing order of Hydrogen-ion concentration
Ques.36 Equal lengths of Magnesium ribbons are taken in test tubes A and B. HCl is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. Amount and concentration taken for both the acids are same. In which test tube will the fizzing occur more vigorously and why?
Ans.36 In test tube A, the fizzing occurs more vigorously than in B because HCl is a strong acid and acetic acid is a mild acid.
Ques.37 Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain?
Ans. When milk turns into curd, lactic acid is formed from the milk sugar, lactose. So, the pH of the curd will become less than the pH of milk and will reduce to around 4.
Ques.38 What is a neutralization reaction? Give example?
Ans.38 It is the reaction between an acid and base to form salt and water.
e.g HCl + NaOH —–> NaCl +H2O
Ques.39 What are hydrated salts? What is water of crystallization?
Ans.39 Hydrated salts are salts which have a fixed no. of water molecules attached with one molecule of salt.
The molecules of water attached to a salt is called water of crystallisation.
E.g Copper sulphate.5H2O (Blue)
Ferrous sulphate.7H2O ( light green)
Ques.40 State preparation, properties and application of following compounds.
Washing Soda, Baking Soda, Bleaching Powder, Plaster of Paris, Sodium Hydroxide.
Ans.40 (a) Washing soda : (Na2CO3 +10H2O —> Na2CO3.10H2O)
|—> It is obtained by heating baking soda and its re –crystallization||—> It is a basic salt which has cleansing action.||—> It is used as a cleaning agent. So, it is a washing powder.
—> It is used in glass, soap and paper industry.
—> Used in manufacture of Borax.
2NaHCO3 Heat____> Na2CO3 + CO2 + H2O
(b) Baking Soda
NaCl + H2O + CO2 + NH3 —-> NH4Cl + NaHCO3
|—-> It is produced using sodium chloride as one of the raw materials.
—-> Its other name is Sodium Hydrogen Carbonate.
|—-> It is a mild base.
—-> Non-Corrosive basic salt.
—-> It is an ingredient in antacids.
|—-> Used in kitchen for making tasty crispy pakoras.
—-> Used for baking purpose.
—-> It is used in soda-acid fire extinguisher.
(c) Bleaching Powder (CaOCl2) (Calciumoxychloride)
Ca(OH)2 +Cl2 —-> CaOCl2 + H2O
|—-> Chlorine is produced during the electrolysis of (aq) sodium chloride. This chlorine gas is used to manufacture bleaching powder. It is produced by the action of chloride or Ca(OH)2||—-> It shows bleaching action due to presence of O2.||—-> Used for bleaching cotton and linen in textile industry, for bleaching wood pulp in paper factories and bleaching washed clothes.
—-> Used as an oxidising agent.
—-> For disinfecting water to make it free of germs.
(d) Plaster of Paris
|—-> On heating gypsum at 373K, it loses water molecules and become Calcium Sulphate hemihydrates.||—-> It is a white powder and on mixing with water, it changes to gypsum giving hard solid mass.||—-> It is used for making toys, materials for decoration and for making surfaces smooth. It is used by doctors in the case of fracture.|
(e) Sodium Hydroxide (NaOH)
|—-> When electricity is passed through NaCl(aq), it decomposes to form NaOH. This process is also called Chlor-Alkali Process.||—-> Cl2 gas is given out at anode and H2 gas at cathode. All the 3 products are very useful. NaOH is basic bitter and soapy.||—-> Used de-greasing metals, used in soaps and detergents. Also used in making artificial fibre.|
2NaCl + 2H2O —-> 2NaOH + Cl2 + H2
Ques.41 What is the difference between baking soda and baking powder?
Ans.41 Baking soda is Sodium Hydrogen Carbonate powder. (NaHCO3)
Baking powder is mixture of baking soda and a mild acid like tartaric acid.
Ques.42 State the function of tartaric acid in baking powder?
Ans.42 When baking soda is heated it converts in sodium carbonate which gives a bitter taste. The acid in baking powder helps in neutralising this and converting it into a sodium salt of the acid.
NaHCO3 + H+ —-> CO2 + H2O + sodium salt
Ques.43 What is common name of salt CaOCl2?
Ans.43 Bleaching powder
Ques.44 Name the substance which on treatment with chlorine yields bleaching powder?
Ans.44 Dry slaked lime
Ques.45 Name the sodium compound which is used for softening hard water?
Ans.45 Washing Soda
Ques.46 What will happen if sodium hydrogen carbonate is heated?
Ans.46 When NaHCO3 is heated it forms sodium carbonate, water and carbon dioxide gas.
2NaHCO3 Heat____> Na2CO3 + CO2 + H2O
Ques.47 Write an equation to show the reaction between plaster of paris and water?
CaSO4.1/2 H2O + 11/2 H2O —-> CaSO4 + 2H2O
Ques.48 Plaster of paris should be stored in a moisture proof container. Why?
Ans.48 Plaster of Paris should be stored in a moisture proof container otherwise it will absorb moisture and will turn into solid hard-mass, Gypsum.
CaSO4.1/2 H2O + 11/2 H2O —-> CaSO4 + 2H2O
Ques.49 What happens when blue copper sulphate salt is heated?
Ans.49 When the blue copper sulphate is heated it loses its water of crystallization and becomes white in colour, when we add water to this salt it again get back its blue colour.
Ques.50 What is water of crystallization?
Ans.50 Water of crystallization is the fixed number of water molecules present in one formula unit of a salt.