2HBr + H2S04-? H2O + Br2 + SO2 Br2 can produce an orange vapor. If F is present,

Question

2HBr + H2S04-? H2O + Br2 + SO2 Br2 can produce an orange vapor. If F is present, the following reactions will occur. Nal + H,S04-NaHSO, t HI 2HI + H2so,-? H2O + I2 + so, 12 will give a purple color and/or black solid. Questions Explain using specific examples how the results follow the expected trend "the larger the pKp value, the more precipitate formed." A 1 ml solution of 0.1 M NaOH is added to 1 ml. of a 0.01 M Ca solution. Predict by aQ calculation whether a precipitate should form. Be sure to consider the dilution effect in your calculation. pK, for Ca(OH), 5.2 1. 2. 3. Why are the observations you made when you added acid (HNO,) to the metal-oxalate precipitates in Part 1-A (step 7) as expected? Hint: consider the magnitude of the pK, , values.

Explanation / Answer

The dissolving equilibrium for Ca(OH)2 is:

Ca(OH)2(s) <--> Ca2+(aq) + 2 OH-(aq)

The equation for Ksp is:
Ksp = [Ca2+][OH-]2= 10-5.2= 6.31 x 10-6

Now calculating the concentration of each ion in the combined solution,

Using relation: M1V1 = M2V2 we get,

[OH-] = (1 mL x 0.1 M) / 2 mL = 0.05 M

[Ca2+] = (1 mL x 0.01 M / 2 mL = 0.005 M

Now calculating the value of Q,

Q = [Ca2+][OH-]2
Q = (0.005) (0.05)2= 1.25 x 10-5

Since Q > Ksp, a precipitate will form.

Thank you

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