Question

PLZ HELP CHEMISTRY! WILL REWARD! Please correct me if I'm wrong.

I marked my answers as x.

1. During a titration, 50.0 ml of 0.2M NaOH were required to neutralize 50.0ml of H3PO4. What's the concentration of the H3PO4 solution?

A. 1.8M
B. 0.6M
C. 0.07M
x D. 0.2M

2. Attached photo - Using the two cell reduction potentials shown for their corresponding reaction, calculate the cell potential for a voltaic cell made from these two systems.

A. –1.68 V
B. –0.78 V
C. 0.78 V
D. 1.68 V

3. If atoms from two different elements react to form a compound, the element with a higher _______ will have a negative oxidation number.

A. atomic number
B. atomic radius
C. energy
x D. electronegativity

4. During the electrolysis of an aqueous solution of sodium nitrate, a gas forms at the anode, what gas is it?

x A. Oxygen
B. Hydrogen
C. Sodium
D. Water


5. The lithium-ion in a lithium-ion battery moves from one side to the other by

A. moving through the cathode.
B. moving through the anode.
x C. passing through the separator.
D. passing through the device.

6. The use of water in a heat exchanger is taking advantage of water's

x A. high specific heat.
B. significant expansion during boiling.
C. solid state when frozen.
D. polar molecular nature.

Which of the following goes through the largest volumetric change?

A. Water when it boils into steam
x B. Water when it freezes into ice
C. Water when it's heated from 1oC to 99oC
D. Ice when it melts into water

Answer 1

Option
`C. \:\:0.07 \:M` is the right choice.

Step-by-step explanation:

Write down the equation and balance it.

`3NaOH+H_3PO_4\Rightarrow \:Na_3PO_4+3H_2O`

For one mole of phosphoric acid, we need three moles of sodium hydroxide.

Concentration of
`NaOH`
`=Molarity=(moles)/(Volume)`

Mole of
`NaOH`
`= 0.2* 50* 10^(-3)`

`=0.01\:moles`

Moles of
`H_3PO_4=(0.01)/(3)=0.0033\:moles`

Finally:

Concentration of
`H_3PO_4=(0.0033)/(0.05)=0.067\:M`