Topic 2

Shorelines often have sediments deposited. The size of particles on these shorelines can vary considerably from one shore to another, as shown here, or within one shoreline. With the tide at or near low tide, use the long measuring tape or line to mark out a transect Fill one of the sample containers at 0m as close to the line as possible. Label this container with the distance it was collected from. Repeat this at regular intervals along the transect. Remove the lid from each container and place all the samples into an oven set at a low temperature to help the water evaporate. Leave for a few days. When the samples are dry use a balance to measure 100 g of sediment from the first sample. If the particles are very large it may not be possible to obtain exactly 100g. Use the grading sieves to separate the sample into different sizes. Use the balance to measure the mass of sediments within each grade. Record your result in a results table. Repeat this for each of the other 4 samples collected. For any samples of sediment which are mostly larger than 5 mm diameter (or whatever the largest sieve size is) these can be graded using callipers. Use a set of callipers to measure both the smallest and largest diameter of a sample of stones. Repeat this for 5 pieces of sediment from each location. The particle size on a shore can affect other conditions such as speed it dries out or how easy it is for animals to burrow into it.

The average salinity of water in oceans is 35 parts per thousand.

The salinity of seawater varies from less than 10 ppt in the Baltic Sea…

…to as high as 280 ppt in the Dead Sea. This investigation uses precise measurements of both the mass and volume of different samples of water of different salinities to calculate the density of these water samples.

To obtain precise results you must use a balance that measures to at least 0.1 g increments. If more precise balances are available, these will give more precise results.

The measuring cylinders must be small enough so that the volume of water samples can be measured to 0.1 cm3 increments. Suitable alternative equipment may include 10 cm3 syringes or burettes

Label one of the measuring cylinders with ’50 ppt salt water’. Label the other measuring cylinder with ‘distilled water’. This will help you to avoid any accidental mixing of the salt water and distilled water which may affect your results.

Use the ‘salt water’ measuring cylinder to measure exactly 10 cm3 of 50 ppt salt water . Check the level of the meniscus carefully to ensure the volume is accurate.

Place the beaker on the balance and zero the balance by pressing the tare or zero button.

Add all the salt water from the measuring cylinder into the beaker – take care not to spill any as this will affect the results.

Record this mass in a results table.

Repeat this process at least 2 more times to collect 3 sets of data for the 50 ppt salt water.

Finally calculate an overall mean for the mass of the 50 ppt sample by adding the three values for each trial and dividing the total by three.

Then calculate the density of the water by dividing the mean mass of the water sample by the volume, which was 10 cm3.

Now we will use a combination of the 50 ppt salt water and distilled water to produce samples of different salinities.

Measure 8 cm3 of 50 ppt salt water using the measuring cylinder labelled to measure this in.

Then measure 2 cm3 of distilled water using the other measuring cylinder we labelled earlier.

When added together this will produce a a more dilute solution of salt, with a concentration of 40 ppt.

Place the beaker on the balance and zero the balance by pressing the tare or zero button.

Add all the salt water from the first measuring cylinder into the beaker, and all of the distilled water from the second measuring cylinder – taking care not to spill any.

Record this mass in a results table.

Repeat this process at least 2 more times to collect 3 sets of data for the 40 ppt salt water…

… and calculate an overall mean for the mass of the 40 ppt sample, and calculate the density of the water.

Now we will just use distilled water to produce a sample of 0 ppt.

Measure 10 cm3 of distilled water using the measuring cylinder labelled to measure this in.

Place the beaker on the balance and zero the balance by pressing the tare or zero button.

Add all of the distilled water from the measuring cylinder – taking care not to spill any.

Record this mass in a results table.

Repeat this process at least 2 more times to collect 3 sets of data for the 0 ppt salt water.…

… and calculate an overall mean for the mass of the 0 ppt sample, and calculate the density of the water.

Different densities of water can result in the formation of layers in seas and oceans. We can show this by colouring samples of 50 ppt water and distilled water and carefully adding them to each other…

…the distilled water is less dense so this floats on top of the more saline water. Changes in density of water due to salinity or temperature differences can result in the formation of vertical currents where denser more saline water sinks.

These vertical currents can help to drive the global ocean conveyor of ocean currents around all the oceans.

Start by making up a concentration of salt water.

For this experiment make a stock solution of 40ppt salt water from which further dilutions will be made.

Begin by adding about 400 cm3 of distilled water to a 500 cm3 measuring cylinder.

Next weigh 20.0g salt out on an electronic balance, accurate to at least 1 decimal place.

Pour the salt into the measuring cylinder of distilled water and mix thoroughly. Top up the volume of solution to 500 cm3 exactly then mix again to produce the stock solution. This can then be poured into a large beaker or other container.

Label the beaker as ‘Saline solution 40ppt’.