Chemistry: Acids and Bases multiple choice help?

Question

I need some help with my homework because my teacher left for vacation early and the sub doesn't know anything :P 

a conjugate acid is an acid that forms when 
a. the acid gains a proton
b. a base loses a proton
c. a base gains a proton
d. both (a) and (b)

an amphoteric species will accept a proton in the presence of a 
a. strong acid
b. strong base
c. both (a) and (b)
d. none of the above

what is the [H3O+] in a of a .0040 M solution of NaOH. (not a typo on my part, that's literally what it says on my paper)
a. 2.5 x 10^-11 M
b. 4.0 x 10^-11 M
c. 2.5 x 10^-10 M
d. 4.0 x 10^-10 M

if the pH of a solution is increased from 2.0 to 4.0, the [H3O+] concentration
a. decreases by a factor of 2 
b. decreases by a factor of 100
c. increases by a factor of 3
d. increases by a factor of 1000

a strip of universal pH paper 
a. is a convenient measure of pH
b. is a precise measure of pH
c. must be calibrated with a pH meter
d. shows very little color change over a wide pH range

a pH meter measures the pH of a solution by measuring the
a. amount of charge on the hydronium ion
b. color of a solution
c. concentration of a solution
d. voltage difference between two electrodes in the meter's probe

thank you very much for your help. fyi, this is from a set of 20 question, the rest of which i managed to solve. these sort of tripped me up and im seeking some confirmation. so no bs about me not doing my homework :P

Anonymous · Accepted Answer

3a 
NaOH dissociates completely so 0,0004 M of NaOH will give you 0,0004 M of OH- ions in solution.
you can calculate the pOH of the solution which is -log [OH-] =pOH  ;  14 - pOH = pH  ;  10^-pH you find answer a (you sure it's not 0,0004? because 0,004 would be [H3O+] = 2,5 X 10^-12 if I'm not mistaken... anyway a or c for sure. (pretty sure it's a)

4b
pH is a logarithmic scale which mean variation of one means variations of 10^1, and so on...  when pH raises, it becomes less acidic [H3O+] go down 100 times 10^2

5b
if i remember right (high school) they turn a color when in base and another in an acid (which is very imprecise but convenient)

6d
the two electrodes are placed in a electrolyte solution (like KCl) and the pH outside makes the electric current between electrodes vary which is interpreted as pH after calibration in known pH solutions

Anita · Answer

1. (b)
Bases gains a proton and become a conjugate acid
eg. HCl (aq) + H2O (l) -> Cl^- (aq) + H3O^3+ (aq)
in this case, H2O is a base and gains a proton to become H3O^3+. therefore the conjugate acid of H2O is H3O^3+

2. (a) <- not 100% if this is correct haha
amphoteric species are things (<-lol) that can act as a base OR acid.
they're usually weak acids/bases (eg. H2O) so i'm assuming that the other thing will have to be strong :)

someone else answered the rest below hahah :)

Raleigh · Answer

1. C
2. A
3. its actually 2.5x10^-12
4. B
5.A?
6. D

Chemistry: Acids and Bases multiple choice help?

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