Question

1. A common cooking technique calls for adding salt to boiling water. Boiling requires heat to overcome the molecular attractions between water molecules so that they can “jump” into the air. After hearing this you think of 2 reasons this might be: 1. saltwater boils faster and 2. saltwater boils hotter. As a scientist, you are hesitant to accept either idea without empirical evidence. Thus, you plan to test these hypotheses by collecting two equivalent pots, fill one with a liter of water and the other with a liter of salted water, and then measure the temperature at which each appears to boil. Answer the following prompts about the experiment:

1. Circle the two hypotheses in the text above.
2. Write your predictions for the outcome of the specific test described in the text.

3. Which of the predictions in part B is the do you think is the most likely outcome and why?

4. The outcome is that saltwater boiled at 215F while the plain water boiled at 210F. Which hypothesis is supported and what is your evidence?

5. Is a hypothesis refuted, evidence?

Answer 1

ANSWER:-

A).

Saltwater boils Hotter.

B).

Saltwater will not boil faster. Salt increases the waters boiling point (above 100 degree celcius) or increases the temparature in order to boil the water. The saltwater solution needs more heat to get hot than a normal water. The time it takes to boil the saltwater increases slightly. So even if the saltwater may be hotter, but it will not boil any faster.

C).

When salt is added to the water, it makes harder for the water molecules to escape from the pot and enters the gas phase. The water molecules enters the gas phase only when the water boils. This gives the salt water a highehr boiling point and lower the specific heat. These changes actuallywork against each other. Raising the boiling point will slower the time of boiling. If we try to get higher temparature that means more time on the stove.

D).

Experiment:-

One pot is filled with one litre of salt water and other pot with one litre plain water. After boiling the outcome is that saltwater boiled at 215F while the plain water boiled at 210F.

• The hypothesis that is supported in this experiment is 'Saltwater boils hotter'.
• The reason is When you add salt to water, sodium chloride diddociates into sodium and chlorine ions. These charged particles alter the intermolecular forces between water molicules, there is an ion-dipole interaction to consider: Every water molecule is a dipole, which means one side (the oxygen side) is more negative and the other side (the hydrogen side) is more positive.
• The positively charged sodium ions align with the oxygen side of a water molecule, while the negatively charged chlorine ions align with the hydrogen side.
• The ion-dipole interaction is stronger than the hydrogen bonding between the water molecule, so more energy is needed to move water away from the ions and into the vapor phase.
• Even without a charged solute, adding particles to water raises the boiling point because part of the pressure the solution exerts on the atmosphere now comes from solute particles, not just solvent (water) molecules.
• The water molecules need more energy to produce enough pressure to escape the boundary of the liquid. The more salt (or any solute) added to water, the more you raise the boiling point.

E).

• The hypothesis that is refuted here is 'saltwater boils faster' because adding salt to water actually raises the boiling point of the water, due to the phenomenon explained above but it also males the waterboils faster.
• Adding any non-volatile solute to a liquid causes a decrease in the liquid's vapour pressure.
• A liquid boils when the vapour pressure above it equals atmospheric pressure, so a lower vapour pressure means you need a higher temperature to boil the water.
• The real reason salt makes water boil faster has to do with specific heat capacities, or the energy it takes to raise the temperature of a substance,
• Salt ions dissolved in water bind to water molecules, holding them stable and making it harder for them to move around.
• As a result, the non-salt bound water molecules receive more of the energy provided by the stove, and boil quicker.
• So adding salt makes it take longer for the water to boil.

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