Urgent Chem Help?

Question

If 1.85 G of cinnamic acid were dissolved in 25 mL (0.025 liters) of H20, what would be the ginal concentration of the solution?

Then:

The Ka. for cinnamic acid is 3.47x10^-5, what is the pH of the above solution?

I'm a complete dunce at chemistry, so please please at least answer the first one and then help me with the second. Thanks mucho

It's HC9H7O2, I figured out the molar mass to 148. I think I got the first part right, with a concentration of .5, but I'm not sure. still need your help please.

Answer 1

question 1
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im guessing you want molar concentration. in that case, you'll need to convert the grams of acid into moles. the formula of the acid is C9H8O2. therefore the molar mass is 148.

to get the moles of acid, you divide the mass of the acid by the molar mass:

moles = mass / molar mass = 1.85 g / 148 g/mol = 0.0125 mol

now to get the molar concentration, divide the moles of acid by the volume of solution:

M = mol / V = 0.0125 mol / 0.025 L = 0.5 mol/L

Question 2
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to get the pH, we'll need to know the H3O+ concentration of the solution. let's start by writing the reaction of the acid with water. I'll represent the acid by HA:

HA + H2O ----> H3O+ + A-

Ka = [H3O+][A-]/[HA]

keep in mind that, according to the balanced equation above, [A-] = [H3O+], so our Ka equation becomes:

Ka = [H3O+][H3O+]/[HA]

which we can write as:

Ka = [H3O+]^2/[HA]

now solve for: [H3O+]

[H3O+] = SQRT(Ka x [HA])

The Ka is given, and [HA] is the molar concentration of the acid, which we already figured out is 0.5 mol/L. so plug those number in:

[H3O+] = SQRT(3.47 x 10^-5 x 0.5) = 0.0042

now use the pH equation to get the pH:

pH = -log [H3O+] = -log(0.0042) = 2.38

Answer 2

with the grams given you need to convert those grams into moles of cinnamic acid. you do that by finding the molecular weight then u divide the given number of grams over the molecular weight and that will give you moles. those moles are then divided by the 0.025 L of water because u need to find the concetration since concentration (molarity) equals moles/L. Then after u have the molarity u can set up an ice table that basically states the connection between ka and the acid. U have to then divide the ka value by the molarity that u calculated and that will give the molarity of the acid. The reason that the ka value is given is because the acid is not a strong one. u need to use the formula pH=-log[H], that is just take the log of the new molarity and that will give you the pH. Remember acids have pH lower than 7. good luck.

Answer 3

I'm a complete dunce at trivial names for compounds, if you have the chem formula, it would be most helpful.