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

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:

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?

The bicarbonate buffer system in the blood is a system evolved to reduce the change in the blood's $\mathrm{pH}$. The system is based around the bicarbonate ion $\left(\mathrm{HCO}_3{ }^{-}\right)$. The equilibrium is: $\mathrm{CO}_2+\mathrm{H}_2 \mathrm{O} \rightleftharpoons \mathrm{H}_2 \mathrm{CO}_3 \rightleftharpoons \mathrm{HCO}_3{ }^{-}+\mathrm{H}^{+}$.

(a) What would be the effect of adding an acid $\left(\mathrm{H}^{+}\right)$to the system?

(b) How does adding the acid affect the blood's $\mathrm{pH}$ ?

(c) How is any acid added to the system ultimately removed? Explain your answer:

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

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:

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

How many times greater is the $\mathrm{H}^{+}$concentration in a $\mathrm{pH} 3$ solution than a $\mathrm{pH} 4$ solution?

It is useful to note at this stage that as $\left[\mathrm{H}^{+}\right]$increases $\left[\mathrm{OH}^{-}\right]$decreases at the same rate. This can be seen in the equation $\left[\mathrm{H}^{+}\right]\left[\mathrm{OH}^{-}\right]=1 \times 10^{-14}$. This value is referred to as $\mathrm{K}_{\mathrm{w}}$ and is constant.

Thus if $\left[\mathrm{H}^{+}\right]=1.0 \times 10^{-1}$ then $\left[\mathrm{OH}^{-}\right]=1 \times 10^{-14} \div 1.0 \times 10^{-1}=1.0 \times 10^{-13}$.

Why do you think a primary standard typically has a high molar mass?

What is pressure?

A bulls-eye target analogy is often used to represent the difference between accuracy and precision (assuming the bullseye is the true value or point). Draw dots on each of the four targets below to describe the four situations:

Consider the following equation: $2 \mathrm{O}_{3(\mathrm{~g})} \rightleftharpoons 3 \mathrm{O}_{2(\mathrm{~g})} \Delta \mathrm{H}=-285 \mathrm{~kJ}$. Describe the effect of the following changes in conditions on the number of $\mathrm{O}_{2(\mathrm{~g})}$ molecules in the system:

(a) The pressure is increased:

(b) The temperature is increased:

(c) $\mathrm{O}_3$ is removed from the system: