Sodium carbonate $\left(\mathrm{Na}_2 \mathrm{CO}_3\right)$ placed in water forms a basic solution. Carbonic acid $\left(\mathrm{H}_2 \mathrm{CO}_3\right)$ in water forms an acidic solution. Use equations to explain these results:

The mass to charge ratio of an isotope was found to be $2.0 \times 10^{-7}$ kilograms per coulomb. If the charge on the isotope is $1.6 \times 10^{-19}$ coulombs, what is the mass of the isotope? HINT: Determine the ratio and cross multiply as usual.

(a) What is the effect of running the system at a high temperature?

(b) What is the effect of then lowering the temperature?

A student set up an equilibrium by dissolving the slightly soluble solid calcium hydroxide in water:

$$\mathrm{Ca}(\mathrm{OH})_{2(\mathrm{~s})} \rightleftharpoons \mathrm{Ca}^{2+}{ }_{(\mathrm{aq})}+\mathrm{OH}_{(\mathrm{aq})}^{-}$$

The student wishes to shift the equilibrium so that more calcium hydroxide dissolves into the solution. He has the following available: nitric acid $\left(\mathrm{HNO}_3\right)$ and calcium nitrate $\left(\mathrm{Ca}\left(\mathrm{NO}_3\right)_2\right.$ - Which of these solutions should the student use and why?

(a) Describe the rate of the forward reaction compared to the backward reaction at the start of reaction A:

(b) Describe the rate of the forward reaction compared to the backward reaction as reaction A neared and then reached equilibrium:

(c) What happened in reaction B when more reactant was added to the reaction?

$\mathrm{NH}_3$ 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:

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 $=11,340 \mathrm{~kg} / \mathrm{m}^3$ ):

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:

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

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

(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?

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?

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:

Why is a compromise of 200 atmospheres and 400C used in the production of ammonia?

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?