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CGB IGCSE Chemistry
Answers Acids and Bases
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Acid and Alkali Problems

Acids and Alkalis

 

1.  What does corrosive mean?

             Corrosive means that the substance can eat away metals, skin, cloth and other substances

2.  How would you test a substance, to see if it is an acid?

            To test a substance to see if it is an acid you could use litmus paper.  Blue litmus paper turns red when put in acid.  Universal indicator turns red or pink when put in acid.

3.  Write down the formula for:

   sulphuric acid

   calcium  hydroxide

   nitric acid

   ammonia solution

             sulphuric acid H2SO4

            calcium hydroxide Ca(OH)2

            nitric acid HNO3

            ammonia solution NH3

4.  What effect do alkalis have on litmus solution?

            Alkalis turn litmus solution blue and turn red litmus paper blue.

5.  Say whether a solution is acidic, alkaline or neutral, if its pH number is:

     9    4    7    1    10    3

            pH 9 Alkali

            pH 4 Acid

            pH 7 Neutral

            pH 1 Acid

            pH 10 Alkali

            pH 3 - Acid

6.  What color would universal indicator show, in an aqueous solution of sugar?  Why?

            Univeral indicator would show a green color in an aqueous solution of sugar because the solution is neutral and the color for neutral is green.

 

7.      Name the acid found in:

Lemon juice      wine     ice tea  vinegar

 

            The acid found in lemon juice is citric acid

            The acid found in wine is ethanoic acid

            The acid found in ice tea is tannic acid

            The acid found in vinegar is ethanoic acid

 

8.      Write a word equation for the reaction of dilute sulphuric acid with :

a.       Zinc

b.      Magnesium oxide

c.       Sodium carbonate

 

Sulphuric acid + zinc zinc sulphate + hydrogen

Sulphuric acid + magnesium oxide magnesium sulphate + water

Sulphuric acid + sodium carbonate sodium sulphate + carbon dioxide + water

 

9.      Bath salts contain sodium carbonate.  Explain why they fizz when you put vinegar on them.

 

Bath salts fizz when you put vinegar on them because bath salts contain sodium carbonate.  When acids and sodium carbonate react they produce a salt, carbon dioxide and water.  Therefore the fizzing occurs due to the creation of carbon dioxide gas.

 

10.  What causes the acidity in acids?

 

The acidity in acids is caused by the H+ ions.  The more H+ ions, the stronger the acid and the greater the acidity.

 

11.  Why is ethanoic acid called a weak acid?

 

Ethanoic acid is called a weak acid because only some of the molecules form ions. 

 

12.  Name two other weak acids, and two strong acids.

 

Two weak acids are : tannic acid and citric acid

Two strong acids are : Hydrochloric acid and Sulphuric acid

 

13.  Which ion do alkalis all have in common?

 

All alkalis form OH- ions.

 

14.  What color would litmus solution turn, if you mixed it with ajax?  Why?

 

Ajax is a alkali solvent.  Therefore litmus solution would turn blue when mixed with ajax.

 

15.  A 10% solution of potassium hydroxide has a higher pH number than a 10% solution of ammonia.  Why is this?  Which one will be a better conductor of electricity.

 

Potassium hydroxide has a higher pH number than ammonia, even though they are the same concentration, because potassium hydroxide is a stronger acid.  When dissolved in water, nearly all the potassium hydroxide molecules form ions.  Potassium hydroxide will be a better conductor of electricity because it has more ions.

 

16.  Write a word equation for the reaction between sodium hydroxide and ammonium chloride.

 

Sodium hydroxide + ammonium chloride sodium chloride + water + ammonia

 

17.  What happens to:

 

a.       The H+ ions

b.      The temperature

Of the solution when an acid is neutralized.

 

When a solution is neutralized the H+ ions combine with the OH- ions in alkalis to form water.  The temperature increases during a neutralization reaction because it is an exothermic reaction.

 

18.  Write a balanced equation for the reaction between sodium hydroxide and

a.       Sulphuric acid

b.      Nitric acid

 

H2SO4 + 2NaOH Na2SO4 + 2H2O

HNO3 + NaOH NaNO3 + H2O

 

19.  What is a base?  Name six bases.

 

A base is a substance that can neutralize an acid.  Bases include:

            Metal oxides CuO, MgO

            Metal hydroxides Ca(OH)2

            Metal carbonates Na2CO3

            Metal hydrogen carbonates NaHCO3

            Ammonia solution NH3

 

20.  What special property do alkalis have?

 

Alkalis are bases which are soluble in water.

 

21.  Which bases react with acids to give carbon dioxide?

 

Metal carbonates react with acids to give carbon dioxide.

 

22.  Write a word equation for the reaction between:

 

a.       dilute hydrochloric acid and copper (II) oxide

b.      dilute sulphuric acid and potassium carbonate

 

Hydrochloric acid + copper(II)oxide copper(II)chloride + water

Sulphuric acid + potassium carbonate potassium sulphate + carbon dioxide + water

 

23.  Write a word equation for the reaction that takes place in your stomach, when you take baking soda to cure indigestion.

 

Your stomach contains hydrochloric acid.  The chemical name for baking soda is sodium hydrogen carbonate.

 

Hydrochloric acid + sodium hydrogen carbonate sodium chloride + carbon dioxide + water