Answer:
21.2 g
Explanation:
Step 1: Given data
- Molar concentration of the solution (C): 0.400 mol/L
- Volume of solution (V): 500 mL (0.500 L)
Step 2: Calculate the moles of Na₂CO₃ (solute) in the solution
We will use the definition of molarity.
C = moles of solute / liters of solution
moles of solute = C × liters of solution
moles of solute = 0.400 mol/L × 0.500 L = 0.200 mol
Step 3: Calculate the mass corresponding to 0.200 moles of Na₂CO₃
The molar mass of Na₂CO₃ is 105.99 g/mol.
0.200 mol × 105.99 g/mol = 21.2 g
Answer:
Phenolphthalein is an indicator. It is pink in alkaline solutions and turns colourless as the pH decreases.
It can be used to measure the activity of the enzyme lipase on the breakdown of lipids.
Samples of milk containing phenolphthalein were incubated with lipase at different temperatures.
The time taken for the phenolphthalein to turn colourless was recorded and used to calculate the rate of enzyme activity.
Figure 10 shows these results.
Picture
(a) (i) Explain why phenolphthalein turns colourless when lipase breaks down the lipids in milk. (2)
(ii) Describe the effect of temperature on the activity of lipase, as shown in Figure 10. (2)
(iii) Explain why the activity of lipase changes above a temperature of 40°C. (2)
(b) A student investigated the time taken for amylase to breakdown a 10% starch solution into glucose at 37°C. The student repeated the investigation five times.
The answer is d
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