Q: A 225 g sample of water is heated from 25.0 °C to 100.0 °C. How much heat (in joules) is required? (Specific heat of water = $$4.184 \ \mathrm{J/g\ ^\circ C})$$

$$q = 225 \times 4.184 \times (100.0 - 25.0) = 70,530 \ \mathrm{J}$$

Question 1

Which property of water explains why ice floats on liquid water?

Accepted Answer

Water expands when it freezes, making ice less dense than liquid water.

Question 2

Which equation correctly represents the amount of heat required to raise the temperature of a substance?

Accepted Answer

$$q = mC\Delta T$$

Question 3

A 225 g sample of water is heated from 25.0 °C to 100.0 °C. How much heat (in joules) is required? (Specific heat of water = $$4.184 \ \mathrm{J/g\ ^\circ C})$$

Accepted Answer

$$q = 225 	imes 4.184 	imes (100.0 - 25.0) = 70,530 \ \mathrm{J}$$

Question 4

Which of the following best describes why water is called the 'universal solvent'?

Accepted Answer

Water can dissolve a wide variety of substances due to its ability to form hydrogen bonds.

Question 5

Which of the following is a natural contaminant in water that can cause hard water?

Accepted Answer

Calcium and magnesium salts

Question 6

What is the main environmental effect of acid rain?

Accepted Answer

It lowers the pH of soil, lakes, and streams, causing environmental damage.

Question 7

Which process in the water cycle is responsible for the movement of water from the surface to the atmosphere?

Accepted Answer

Evaporation

Question 8

A baby develops methemoglobinemia (blue baby syndrome) after drinking well water. Which contaminant is most likely responsible?

Accepted Answer

Nitrate ions

Question 9

Which of the following is a correct statement about the U.S. Safe Drinking Water Act?

Accepted Answer

It sets and enforces national health-based standards for contaminants in municipal water supplies.

Question 10

What is the maximum contaminant level for lead in drinking water according to EPA standards?

Accepted Answer

$$0.015 \ \mathrm{mg/L}$$

Question 11

Which of the following best describes the process of coagulation in water treatment plants?

Accepted Answer

Adding slaked lime and alum to form aluminum hydroxide, which removes colloidal particles and bacteria

Question 12

Which chemical reaction represents the formation of aluminum hydroxide during water treatment?

Accepted Answer

$$3 \ \mathrm{Ca(OH)_2(aq)} + \mathrm{Al_2$(SO_4$)_3(aq)} \rightarrow 2 \ \mathrm{Al(OH)_3(s)} + 3 \ \mathrm{$$CaSO_4$$(aq)}$$

Question 13

Why is chlorine commonly added to municipal drinking water?

Accepted Answer

To kill bacteria and provide residual disinfection throughout the distribution system

Question 14

What is the main advantage of using ozone instead of chlorine for water disinfection?

Accepted Answer

Ozone kills many viruses in addition to bacteria.

Question 15

What is the chemical reaction that occurs when fluoride is added to tooth enamel?

Accepted Answer

$$\mathrm{Ca_5$(PO_4$)_3OH(s) + F^-(aq) \rightarrow Ca_5$(PO_4$)_3F(s) + OH^-(aq)}$$

Question 16

Which of the following is a potential negative effect of excessive fluoride in drinking water?

Accepted Answer

Discoloration of teeth (dental fluorosis)

Question 17

Which step in municipal wastewater treatment is primarily responsible for removing large solids and grit?

Accepted Answer

Primary treatment (settling ponds)

Question 18

What is the main purpose of the activated sludge method in wastewater treatment?

Accepted Answer

To use aerobic bacteria to break down organic matter in sewage

Question 19

A city wants to reduce the risk of eutrophication in a nearby lake. Which action would be most effective?

Accepted Answer

Reduce the release of sewage and agricultural runoff into the lake

Question 20

A sample of seawater contains $$3.90 	imes 10$$^{-6}$$ ppm of dissolved gold. How many liters of seawater are needed to obtain 1.00 g of gold? (Assume the density of water is 1.00$$ \ \mathrm{g/mL}$$.)

Accepted Answer

$$2.56 	imes 10^5$ L

Water: Properties, Contaminants, and Treatment in Introductory Chemistry

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