A sample of gas is warmed from 30.0 oC to 90.0 oC at a constant pressure.
Its initial volume is 1.75 liters. What is the final volume of the gas.

A mixture of oxygen, hydrogen, nitrogen and carbon dioxide
In a two liter flask has a total pressure of 1.251 atm.
The partial pressure of oxygen, hydrogen, and nitrogen
Are 0.210, 0.145, and 0.235 atm, respectively. Use Dalton's
Law of partial pressures to determine the partial pressure
Of the carbon dioxide.

Ammonia’s behavior as a weak base is best explained as a

a. a source of hydroxide ions.
b. a proton donor
c. a proton acceptor
d. a nonelectrolyte
e. none of the above.

Would the answer be "c" because base is defined as a proton acceptor?

Hydrogen bonding in water contributes to

a. a decreased boiling point b. an increased vapor pressure
c. a decreased melting point d. an increase in volume on freezing
e. none of the above.

This was on a homework assignment and I put "e" because I wasn't sure. Probably wrong huh?

The pH of many cola ‑ type drinks is about 3.0. How many times
Greater is the hydronium ion concentration in these drinks than
In neutral water?

Changing the temperature of 4.0 mol of hydrogen gas at
Constant pressure from 100 oK to 200 K will

a. increase its mass by a factor of three.
b. decrease the volume that the gas occupies.
c. increase the kinetic energy of the hydrogen molecules.
d. decrease the density by a factor of two.

For this homework question I picked "b" am I correct?

In one experiment, a dry sample of an unknown
Gas was collected. Its volume at 745 mm Hg and
63.0 oC was 815.5 mL. How many moles of this gas
Was obtained?

What is the pH of a solution with a hydronium ion
concentration of 2.40 x 10‑4

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A sample of gas is warmed from 30.0 oC to 90.0 oC at a constant pressure.
Its initial volume is 1.75 liters. What is the final volume of the gas.

i=initial and f=final.

Just use the formula \frac{P_{i}V_{i}}{T_{i}}=\frac{P_{f}V_{f}}{T_{f}}

Since the pressure is constant, we can omit the P's.

Plug your knowns into \frac{V_{i}}{T_{i}}=\frac{V_{f}}{T_{f}} and solve for V_{f}

Changing the temperature of 4.0 mol of hydrogen gas at
constant pressure from 100 oK to 200 K will

a. increase its mass by a factor of three.
b. decrease the volume that the gas occupies.
c. increase the kinetic energy of the hydrogen molecules.
d. decrease the density by a factor of two.

for this homework question i picked "b" am i correct?

Nope. In fact, the volume will increase. You know the formula for ideal gas?

PV=nRT

Well, pressure is kept constant, the number of moles is constant, R is a constant. Only V and T are variables. So, V is directly proportional to T. Since you increase T, you'll have an increase in Volume.

Let's see the others.
a. Mass is constant, since the number of moles is constant.
c. True, upon heating (with no change of state) a substance gets more kinetic energy. It is that energy which gives you the temperature.
d. Since you increased temperature by a factor of 2 (from 100 to 200) the volume will also increase by a factor of 2. Density is inversely proportional to volume when mass is constant, so the density will decrease by a factor of 2.

Something seems wrong here... c and d are correct. Are you sure you didn't make a mistake in typing? Or maybe the temperature is not in Kelvin, then d will not be the answer.

In one experiment, a dry sample of an unknown
gas was collected. Its volume at 745 mm Hg and
63.0 oC was 815.5 mL. How many moles of this gas
was obtained?

Use the formula I just gave you. Be careful though. The formula is valid for the units of Pascal for pressure, metre cube for volume, moles for the number of moles, joules per kelvin per mole for the constant R (which has a value of 8.31) and kelvin for temperature.

What is the pH of a solution with a hydronium ion
concentration of 2.40 x 10‑4

pH is given by the logarithm of the reciprocal of the molar concentration of the hydrogen ion in the solution:

pH = -log(H^+)

Since a hydronium ion has a hydrogen ion, you can take the concentration of the hydronium ion as the concentration of the hydrogen ion.

The pH of many cola ‑ type drinks is about 3.0. How many times
greater is the hydronium ion concentration in these drinks than
in neutral water?

Use the formula for pH I just gave you.

Ammonia’s behavior as a weak base is best explained as a

a. a source of hydroxide ions.
b. a proton donor
c. a proton acceptor
d. a nonelectrolyte
e. none of the above.

would the answer be "c" because base is defined as a proton acceptor?

No. What determines the strength of a base is its ability to dissociate and form hydroxide ions in water. Therefore, the answer is e. Being a proton acceptor doesn't automatically make it a weak base. As you said, the definition of a base is a substance that accepts a proton. All bases are proton acceptors, but some are strong bases, and others weak bases. So, you cannot have c as answer.

A mixture of oxygen, hydrogen, nitrogen and carbon dioxide
in a two liter flask has a total pressure of 1.251 atm.
The partial pressure of oxygen, hydrogen, and nitrogen
are 0.210, 0.145, and 0.235 atm, respectively. Use Dalton's
Law of partial pressures to determine the partial pressure
of the carbon dioxide.

The formula for finding the partial pressure is:

P_{gas} = \frac{n_{gas}}{n_{total}} \times P_{total}

Where P is the pressure, n is the number of moles.

For solving the question more easily, look here.

Partial pressures of gases add up to make the total pressure. Can you therefore find the partial pressure carbon dioxide provides?

I am actually taking an online class and my teacher has been MIA for the past 2 weeks and I really need serious help. I'm a music major and am not very good in chemistry and no one that I know can I really help me with this. I tried calling my teacher and emailing him a ton of times. So although it looks as though I'm mooching I really just want help. Isn't that what this website is about?

And also... some of this questions I posted I had already answered and turned in I just didn't feel good about them and wanted to know if I was correct and how to do it the correct way.

The formula for finding the partial pressure is:

P_{gas} = \frac{n_{gas}}{n_{total}} \times P_{total}

Where P is the pressure, n is the number of moles.

For solving the question more easily, look here.

Partial pressures of gases add up to make the total pressure. Can you therefore find the partial pressure carbon dioxide provides?

so would the partial pressure of carbon dioxide be 0.661 atm?

pH is given by the logarithm of the reciprocal of the molar concentration of the hydrogen ion in the solution:

pH = -log(H^+)

Since a hydronium ion has a hydrogen ion, you can take the concentration of the hydronium ion as the concentration of the hydrogen ion.

- log 2.40 x 10^-4 =3.62

would this be correct?

so would the partial pressure of carbon dioxide be 0.661 atm?

Correct.


- log 2.40 x 10^-4 =3.62

would this be correct?

Correct also.


and also... some of this questions i posted i had already answered and turned in i just didn't feel good about them and wanted to know if i was correct and how to do it the correct way.

It's okay. :)


Hydrogen bonding in water contributes to

a. a decreased boiling point b. an increased vapor pressure
c. a decreased melting point d. an increase in volume on freezing
e. none of the above.

this was on a homework assignment and i put "e" because i wasn't sure. Probably wrong huh?

b. is true, the hydrogen bond will tend to raise the vapor pressure, thereby raising the melting and boiling points.

d. Here, water expands on cooling because the hydrogen bond has a specific length. In the liquid state, hydrogen bonds are constantly being formed and broken by other water molecules passing 'across' the bond. On cooling, since the molecules go slower, there is a lower probability that they will break the hydrogen bond.

So, I think that both b and d are correct.