In glass $B$ (above right) what can you say about the densities of the three substances present?

$\mathrm{NH}_3$ in water reacts to form $\mathrm{NH}_4{ }^{+}$in the equilibrium reaction:

$$\mathrm{NH}_3+\mathrm{H}_2 \mathrm{O} \rightleftharpoons \mathrm{NH}_4^{+}+\mathrm{OH}^{-}$$

(a) Is $\mathrm{NH}_3$ a strong or weak base?

(b) Explain why the $\mathrm{pH}$ of a $\mathrm{NH}_3$ solution is lower than that of a $\mathrm{NaOH}$ solution:

Consider the two acids $\mathrm{HCl}$ and $\mathrm{CH}_3 \mathrm{COOH}$. When in (separate) solutions they react in the following way:

• The $\mathrm{pH}$ of the $\mathrm{HCl}$ was measured at 1. The $\mathrm{pH}$ of the $\mathrm{CH}_3 \mathrm{COOH}$ was measured at $2.88$.
• $25 \mathrm{~mL} 0.1 \mathrm{~mol} / \mathrm{L}$ of each acid was reacted with an excess of sodium carbonate $\left(\mathrm{Na}_2 \mathrm{CO}_3\right)$. The reaction between $\mathrm{HCl}$ and $\mathrm{Na}_2 \mathrm{CO}_3$ was vigorous. The reaction between $\mathrm{CH}_3 \mathrm{COOH}$ and $\mathrm{Na}_2 \mathrm{CO}_3$ was much slower.
• Each reaction produced the same amount of $\mathrm{CO}_2$ gas.

(a) Which acid has the greatest concentration of $\mathrm{H}^{+}$ions in solution?

(b) Explain why the same amount of $\mathrm{CO}_2$ gas was produced despite the $\mathrm{pH}$ of the acids being different:

Methane $\left(\mathrm{CH}_4\right)$ is a gas.

(a) What is the ratio of carbon to hydrogen atoms?

(b) If a methane sample contains 1575 atoms, how many carbon and hydrogen atoms are present? Show your working:

(c) Can a sample of methane contain 1577 atoms? Explain your answer:

Fresh water has a density of $1000 \mathrm{~kg} / \mathrm{m}^3$. Will the following objects sink or float if placed in it?

(a) A cork (density $=240 \mathrm{~kg} / \mathrm{m}^3$ ):

(b) A piece of lead (density $=11,340 \mathrm{~kg} / \mathrm{m}^3$ ):

(a) In which direction does adding heat drive the system?

(b) In which direction does removing heat drive the system?

The following substances are acids or bases. The ions they form in solution are shown:

$$\begin{array}{|c|c|c|} \hline \text { Substance } & \text { Acid/base } & \text { lons in solution } \\ \hline \mathrm{HCl} & \text { Acid } & \mathrm{H}^{+} \mathrm{Cl}^{-} \\ \hline \mathrm{HNO}_3 & \text { Acid } & \mathrm{H}^{+} \mathrm{NO}_3^{-} \\ \hline \mathrm{CH}_3 \mathrm{COOH} & \text { Acid } & \mathrm{H}^{+} \mathrm{CH}_3 \mathrm{COO}^{-} \\ \hline \mathrm{NaOH} & \text { Base } & \mathrm{Na}+\mathrm{OH}^{-} \\ \hline \mathrm{KOH} & \text { Base } & \mathrm{K}_{+} \mathrm{OH}^{-} \\ \hline \mathrm{NH}_3 & \text { Base } & \mathrm{NH}_4{ }^{+} \mathrm{OH}^{-} \\ \hline \end{array}$$

(a) What ion(s) do the acids have in common?

(b) What ion(s) do the bases have in common?

(a) Under what conditions would the first reaction be carried out in order to produce the greatest amount of hydrogen?

(b) To increase the hydrogen produced, the hydrogen is constantly removed from the system. How would this help produce more hydrogen?

Discuss potential sources of error during a volumetric analysis with your lab partners (from making the standard solution to performing the titration). Name them and describe how you would minimize them. Use more paper if you need to:

Ammonia $\left(\mathrm{NH}_3\right)$ is a compound with $1: 3$ ratio of nitrogen to hydrogen atoms.

(a) If a sample of ammonia contains 1500 nitrogen atoms, determine the number of hydrogen atoms present?

Imagine a beaker half full of water (below right). The beaker is sealed with cling wrap. Some of the water will evaporate to form gaseous $\mathrm{H}_2 \mathrm{O}$. At some point the rate of gas forming will equal the rate of condensation.

(a) What might happen to the rate of gas forming if the beaker is warmed by placing it in the sun, or on a heat pad?

(b) How might this affect the amount gas in the system compared to the liquid water?

(c) The beaker is placed in a fridge. What would happen to the rate of gas formation now?

(d) How would this affect the amount of gaseous water compared to liquid water in the system?

Calculating a $95 \%$ confidence interval $(95 \% \mathrm{Cl})$ provides a good estimate of how close the sample mean is to the true mean. The mean $\pm$ the $95 \%$ $\mathrm{Cl}$ gives the $95 \%$ confidence limits. On average, 95 times out of 100 , the true population mean will lie within the confidence limits. The $95 \% \mathrm{Cl}$ can be plotted onto graphs to determine significance. If they overlap there is no significant difference between the data. The $95 \% \mathrm{Cl}$ for student $\mathrm{A}$ is $1.27$ and for student $\mathrm{B}$ is $2.37$ at $\mathrm{p}=0.05$.

(a) Plot the mean dispensing volume and $95 \% \mathrm{Cl}$ for both sets of data on the grid right). Plot as a column graph with error bars.

(b) Is the difference significant? Why or why not?

(a) Explain why the pressure in a sealed container of gas increases when heat is added to the system:

(b) Explain why the pressure in a sealed container of gas decreases when the system is cooled:

A solution of NaOH is made up to 0.25 mol/ L. Calculate its pH: