If carbon dioxide gas (CO2) is dissolved in pure water, what will happen to the pH of the solution?

1.1.17. When carbon dioxide ($\text{CO}_2$) dissolves in pure water, it reacts to form carbonic acid ($\text{H}_2\text{CO}_3$).

$$\text{CO}_2(\text{g}) + \text{H}_2\text{O}(\text{l}) \rightleftharpoons \text{H}_2\text{CO}_3(\text{aq})$$

Since carbonic acid is an acid, it will lower the pH of the solution from the neutral pH of 7.

The correct option is C.

• C. The pH will drop below 7

1.1.18. When phosphorus burns in oxygen, it forms phosphorus pentoxide ($\text{P}_4\text{O}_{10}$), which is an acidic oxide. When this powder dissolves in water, it forms phosphoric acid ($\text{H}_3\text{PO}_4$).

$$\text{P}_4\text{O}_{10}(\text{s}) + 6\text{H}_2\text{O}(\text{l}) \to 4\text{H}_3\text{PO}_4(\text{aq})$$

Acids turn universal indicator red.

The correct option is C.

• C. The indicator will turn red

1.1.19. Acids have several characteristic properties.

• A. Turning red litmus paper blue is a property of bases. Acids turn blue litmus paper red.
• B. A pH value greater than 7 is a property of bases. Acids have a pH value less than 7.
• C. Feeling slippery or soapy to the touch is a property of bases.
• D. Tasting sour is a common property of acids.

The correct option is D.

• D. It tastes sour

1.1.20. A neutral solution is one that is neither acidic nor basic. On the pH scale, a value of 7 indicates a neutral solution.

The correct option is D.

• D. 7

1.1.21. We need to identify which of the given substances is a common household example of a base.

• A. Baking soda (sodium bicarbonate) is a common household base.
• B. Vinegar (acetic acid) is a common household acid.

The correct option is A.

• A. Baking soda