Neutralisation reactions

Classify each of these substances as an acid, a base or a salt:

1. a) $HNO_3$ (nitric acid)
2. b) $KOH$ (potassium hydroxide)
3. c) $NaCl$ (sodium chloride)
4. d) $H_2SO_4$ (sulfuric acid)
5. e) $Ca(OH)_2$ (calcium hydroxide)

pH measures how acidic or basic a solution is. These are the positions of the four solutions on the pH scale:

State whether each of these solutions is acidic, neutral or basic:

1. a) lemon juice, $pH = 2,5$
2. b) pure water, $pH = 7$
3. c) hand soap, $pH = 10$
4. d) crushed tomato, $pH = 4,5$

Complete the general scheme of a neutralisation reaction with the missing words: "An $\dots$ reacts with a $\dots$ to form a $\dots$ and $\dots$". Then give an example using the reaction between hydrochloric acid and sodium hydroxide.

In the laboratory, hydrochloric acid ($HCl$) is mixed with sodium hydroxide ($NaOH$) to form sodium chloride ($NaCl$), common salt, and water. Write the reaction equation and check by counting atoms that it is balanced.

Sulfuric acid ($H_2SO_4$) reacts with calcium hydroxide ($Ca(OH)_2$) to form calcium sulfate ($CaSO_4$) and water. Write the equation and balance it; pay close attention to how many water molecules are formed for each calcium sulfate.

Write and balance the equation for the neutralisation between hydrochloric acid ($HCl$) and calcium hydroxide ($Ca(OH)_2$), forming calcium chloride ($CaCl_2$) and water.

Write and balance the equation for the neutralisation of sulfuric acid ($H_2SO_4$) with sodium hydroxide ($NaOH$), forming sodium sulfate ($Na_2SO_4$) and water.

Gastric juice in the stomach contains hydrochloric acid. In cases of heartburn, antacids from the pharmacy, which contain bases such as magnesium hydroxide, relieve it. Explain, using the concept of neutralisation, how an antacid works in the stomach.

Litmus paper turns red in acidic conditions and blue in basic conditions.

1. a) What colour will it turn in a solution of $HCl$?
2. b) And in a solution of $NaOH$?
3. c) We mix the two solutions in exact amounts for complete neutralisation: explain why the litmus paper no longer indicates acid or base in the resulting mixture.

Write the formula and name of the salt formed in each neutralization reaction:

1. a) Hydrochloric acid ($HCl$) with potassium hydroxide ($KOH$).
2. b) Nitric acid ($HNO_3$) with sodium hydroxide ($NaOH$).

Milk of magnesia is a suspension of magnesium hydroxide ($Mg(OH)_2$) taken for heartburn. Its reaction with stomach acid is $Mg(OH)_2 + 2\ HCl \rightarrow MgCl_2 + 2\ H_2O$.

1. a) How many moles of $HCl$ does $1\ \text{mol}$ of $Mg(OH)_2$ neutralise?
2. b) If the stomach has an excess of $0,1\ \text{mol}$ of $HCl$, how many moles of $Mg(OH)_2$ are needed to neutralise it?

In a laboratory flask, there are $0,2\ \text{mol}$ of sulphuric acid ($H_2SO_4$).

1. a) Write the balanced equation for its neutralisation with sodium hydroxide ($NaOH$), which produces sodium sulphate ($Na_2SO_4$) and water.
2. b) Calculate how many moles of $NaOH$ are needed to neutralise all the acid.
3. c) If we were to add only $0,2\ \text{mol}$ of $NaOH$, would the solution be acidic, neutral or basic? Justify your answer using stoichiometry.