C2- acids, bases and salts

Question 1

What are acids?

Answer 1

Substances with a pH of less than 7 are acids. The more strongly acidic the solution, the lower its pH number.

Question 2

How do acids react with litmus paper?

Answer 2

Acidic solutions turn blue litmus paper red.

Question 3

How do acids react with universal indicator?

Answer 3

They turn universal indicator paper red if they are strongly acidic, and orange or yellow if they are weakly acidic.

Question 4

What are bases?

Answer 4

Substances that can react with acids and neutralise them to make a salt and water are called bases. They are usually metal oxides or metal hydroxides.

Question 5

What are alkalis?

Answer 5

Bases that dissolve in water are called alkalis. Alkaline solutions have a pH of more than 7. The stronger the alkali, the higher the pH number

Question 6

How do alkalis react with litmus paper?

Answer 6

Alkalis turn red litmus paper blue.

Question 7

How do alkalis react with universal indicator?

Answer 7

They turn universal indicator paper dark blue or purple if they are strongly alkaline, and blue-green if they are weakly alkaline.

Question 8

What are neutral solutions?

Answer 8

Neutral solutions have a pH of 7.

Question 9

How do neutral solutions react with litmus paper?

Answer 9

They do not change the colour of litmus paper

Question 10

How do neutral solutions react with universal indicator?

Answer 10

they turn universal indicator paper green

Question 11

What are the four state symbols?

Answer 11

(s) means solid
(l) means liquid (not the same as dissolved in water - see below)
(g) means gas
(aq) means aqueous (dissolved in water)

Question 12

What ions do acids produce when dissolved in water?

Answer 12

When acids dissolve in water they produce aqueous hydrogen ions, H+(aq). For example, looking at hydrochloric acid:

HCl(aq) → H+(aq) + Cl–(aq)

Question 13

What ions do alkalis produce when dissolved in water?

Answer 13

When alkalis dissolve in water they produce aqueous hydroxide ions, OH–(aq). For example, looking at sodium hydroxide:

NaOH(aq) → Na+(aq) + OH–(aq)

Question 14

What is the equation of ammonia in a solution?

Answer 14

NH3(aq) + H2O(l) → NH4+(aq) + OH–(aq) (small numbers)

Question 15

What is the neutralization equation?

Answer 15

H+(aq) + OH–(aq) → H2O(l)

Question 16

What are the equations for when acids react with bases?

Answer 16

acid + metal oxide → salt + water

acid + metal hydroxide → salt + water

Question 17

What is the equation for when an acid reacts with a metal?

Answer 17

acid + metal → salt + hydrogen

Question 18

How can hydrogen be detected?

Answer 18

The hydrogen causes bubbling during the reaction, and can be detected using a lighted splint.

Question 19

How can we predict the name of the salt formed?

Answer 19

The first part of the name is ‘ammonium’ if the base used is ammonia. Otherwise, it is the name of the metal in the base. The second part of the name comes from the acid used:

Chloride (if hydrochloric acid is used)
Nitrate (if nitric acid is used)
Sulfate (if sulfuric acid is used)

Question 20

How do you crystallize salt solutions?

Answer 20

If the base dissolves in water, you need to add just enough acid to make a neutral solution. Check a small sample with universal indicator paper. Warm the salt solution to evaporate the water. You get larger crystals if you evaporate the water slowly.If the base does not dissolve in water, you need an extra step. You add the base to the acid until no more will dissolve and you have some base left over (called an excess). You filter the mixture to remove the excess base, then evaporate the water in the filtrate to leave the salt behind.

Question 21

Are nitrates soluble?

Answer 21

Yes, all of them are.

Question 22

Are sulfates soluble?

Answer 22

Most are, except for Lead sulfate, barium sulfate

Question 23

Are chlorides, bromides and iodides soluble?

Answer 23

Most are, except for Silver chloride, silver bromide, silver iodide, lead chloride, lead bromide, lead iodide

Question 24

Are carbonates soluble?

Answer 24

Most aren’t, except for Sodium carbonate, potassium carbonate

Question 25

Are hydroxides soluble?

Answer 25

Most aren’t, except for Sodium hydroxide, potassium hydroxide

Question 26

How do you make an insoluble salt?

Answer 26

You need to react two soluble salts together in a precipitation reaction. if you want to make an insoluble salt XY, mixing X nitrate with sodium Y will always work. The salt forms a precipitate. The precipitate can be filtered, washed with water on the filter paper, and then dried in an oven.

Question 27

What are the uses of precipitation reactions?

Answer 27

Precipitation reactions can be used to remove unwanted ions in solution. This is useful for treating drinking water and waste water.