Describe the arrangement and movement of particles in a liquid?
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particles are close together but irregularly arranged; particles slide over each other / move around each other
States Of Matter
Explain why a gas fills its container but a liquid does not?
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gas particles have much more kinetic energy than liquid particles; gas particles move rapidly in all directions / random motion; forces between gas particles are negligible so they spread out to fill the available space
State the name of the change of state from gas to liquid?
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condensing / condensation
Explain, in terms of particles, what happens when a solid melts?
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particles gain kinetic energy; particles vibrate more until they break free from their fixed positions; the regular arrangement is lost and particles can slide over each other
Describe how sublimation differs from boiling?
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sublimation is the change from solid directly to gas; boiling is the change from liquid to gas
Explain why a coloured solution becomes paler when water is added, but the colour does not disappear?
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the coloured solute particles spread out / become more spaced out among the water particles; there are still coloured particles present even though fewer are in any given volume
Explain, in terms of particles, why bromine vapour gradually spreads into a jar of air?
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bromine particles move randomly in all directions; they spread from a region of higher concentration to lower concentration / they diffuse; the spreading is gradual because bromine particles collide with air particles
Suggest why hydrogen chloride gas diffuses faster than bromine vapour at the same temperature?
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hydrogen chloride molecules have a lower molecular mass / are lighter than bromine molecules; lighter particles move faster at the same temperature so they diffuse more quickly
Define the term saturated solution?
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a solution that contains the maximum amount of solute; that can dissolve at that temperature
Identify the solvent and solute when sodium chloride dissolves in water?
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solvent is water; solute is sodium chloride
State what is meant by the term solubility?
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the mass of solute that dissolves in 100 g of solvent; at a particular temperature
Calculate the solubility of copper sulfate if 20 g dissolves in 80 g of water at 40 °C?
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Copper sulfate, CuSO₄ State the equation for solubility. $$\text{solubility}=\frac{\text{mass of solute}}{\text{mass of solvent}}\times 100$$ Substitute the given values. $$\text{solubility}=\frac{20}{80}\times 100$$ $$\text{solubility}=25\text{ g per 100 g of solvent}$$
Describe how to use a solubility curve to find the solubility of a substance at 50 °C?
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locate 50 °C on the x-axis and draw a vertical line up to the curve; draw a horizontal line from the curve to the y-axis and read the solubility value
The solubility of substance X at 80 °C is 95 g per 100 g of water, and at 30 °C it is 40 g per 100 g of water. Calculate the mass of crystals formed when a saturated solution made with 200 g of water is cooled from 80 °C to 30 °C?
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Substance X Mass dissolved at 80 °C in 200 g of water. $$\text{mass at 80 °C}=\frac{95}{100}\times 200=190\text{ g}$$ Mass dissolved at 30 °C in 200 g of water. $$\text{mass at 30 °C}=\frac{40}{100}\times 200=80\text{ g}$$ Mass of crystals formed. $$\text{mass of crystals}=190-80$$ $$\text{mass of crystals}=110\text{ g}$$
Predict what happens if more solute is added to a saturated solution at constant temperature?
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the extra solute does not dissolve / remains as a solid at the bottom
Explain why a water bath is used rather than heating the boiling tube directly with a Bunsen burner?
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a water bath provides even, gentle heating; it maintains a constant/steady temperature so the solubility measurement is accurate at a specific temperature
Describe how you would know the solution has become saturated?
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undissolved solid remains at the bottom of the boiling tube after stirring / no more solid dissolves
A student dissolves 7.2 g of potassium chloride in 20 g of water at 40 °C to form a saturated solution. Calculate the solubility of potassium chloride at 40 °C?
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Potassium chloride, KCl State the equation for solubility. $$\text{solubility}=\frac{\text{mass of solute}}{\text{mass of solvent}}\times 100$$ Substitute the given values. $$\text{solubility}=\frac{7.2}{20}\times 100$$ $$\text{solubility}=36\text{ g per 100 g of solvent}$$
Identify the independent variable and one control variable in this experiment?
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independent variable is the mass of solid added; control variable is the temperature of the water / mass of water used