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3 years ago

The mass number for an atom is numerically equal to which quantity

Chemistry

1 answer:

Misha Larkins [42]3 years ago

4 0

Answer:

The mass number of an atom is equal to the number of protons plus the number of neutrons that it contains. In other words, the number of neutrons in an atom is its mass number minus its atomic number.

Explanation:

protons

The mass number of an atom is its total number of protons and neutrons. Atoms of different elements usually have different mass numbers , but they can be the same. For example, the mass number of argon atoms and calcium atoms can both be 40.

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Acetic acid (HC2H3O2, Ka=1.8x10^-5) is a weak acid. Calculate the pH of an aqueous solution of .25M acetic acid.

tensa zangetsu [6.8K]

Answer: The pH of an aqueous solution of .25M acetic acid is 2.7

Explanation:

$HC_2H_3O_2\rightarrow H^+C_2H_3O_2^-$

cM 0 0

$c-c\alpha$ $c\alpha$ $c\alpha$

So dissociation constant will be:

$K_a=\frac{(c\alpha)^{2}}{c-c\alpha}$

Give c= 0.25 M and $\alpha$ = ?

$K_a=1.8\times 10^{-5}$

Putting in the values we get:

$1.8\times 10^{-5}=\frac{(0.25\times \alpha)^2}{(0.25-0.25\times \alpha)}$

$(\alpha)=0.0084$

$[H^+]=c\times \alpha$

$[H^+]=0.25\times 0.0084=0.0021$

Also $pH=-log[H^+]$

$pH=-log[0.0021]=2.7$

Thus pH is 2.7

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3 years ago

Which sample contains more atoms: 3.89 g of nickel or 6.61 g of silver? Defend your answer.

Alenkinab [10]

Nickel contains more atoms

3 0

2 years ago

How many electrons does hydrogen need to satisfy the octet rule?

quester [9]

Just 2 valence electrons.

Hydrogen already has one to start with, as well. With the exception of hydrogen and helium, all other atoms need 8 valence e-

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3 years ago

A piece of wood has a labeled length value of 63.2 cm. You measure its length three times and record the following data: 63.1 cm

Ulleksa [173]

Percent error (%)= $\frac{\left | Accepted value - Measured value \right |}{Accepted value}\times 100$

Accepted value is true value.

Measured values is calculated value.

In the question given Accepted value (true value) = 63.2 cm

Given Measured(calculated values) = 63.1 cm , 63.0 cm , 63.7 cm

1) Percent error (%) for first measurement.

Accepted value (true value) = 63.2 cm, Measured(calculated values) = 63.1 cm

Percent error (%)= $\frac{\left | Accepted value - Measured value \right |}{Accepted value}\times 100$

$Percent error = \frac{\left | 63.2 - 63.1 \right |}{63.2}\times 100$

$Percent error = \frac{0.1}{63.2}\times 100$

$Percent error = 0.00158\times 100$

Percent error = 0.158 %

2) Percent error (%) for second measurement.

Accepted value (true value) = 63.2 cm, Measured(calculated values) = 63.0 cm

Percent error (%)= $\frac{\left | Accepted value - Measured value \right |}{Accepted value}\times 100$

$Percent error = \frac{\left | 63.2 - 63.0 \right |}{63.2}\times 100$

$Percent error = \frac{0.2}{63.2}\times 100$

$Percent error = 0.00316\times 100$

Percent error = 0.316 %

3) Percent error (%) for third measurement.

Accepted value (true value) = 63.2 cm, Measured(calculated values) = 63.7 cm

Percent error (%)= $\frac{\left | Accepted value - Measured value \right |}{Accepted value}\times 100$

$Percent error = \frac{\left | 63.2 - 63.7 \right |}{63.2}\times 100$

$Percent error = \frac{\left | -0.5 \right |}{63.2}\times 100$

$Percent error = \frac{(0.5)}{63.2}\times 100$

$Percent error = 0.00791\times 100$

Percent error = 0.791 %

Percent error for each measurement is :

63.1 cm = 0.158%

63.0 cm = 0.316%

63.7 cm = 0.791%

7 0

3 years ago

A solution is prepared by dissolving 23.7 g of cacl2 in 375 g of water. the density of the resulting solution is 1.05 g/ml. the

alekssr [168]

The density of the solution =1.05 g/ml.
The total mass of the resulting solution is = 398.7 g (CaCl2 + water)

Find moles of CaCl2 and water.
Molar mass of CaCl2 = 110 (approx.)

Moles of CaCl2 = 23.7 / 110 = 0.22
so, moles of Cl- ion = 2 x 0.22 = 0.44 (because each molecule of CaCl2 will give two Cl- ions)
Moles of water = 375 / 18 = 20.83

Now, Mole fraction of CaCl2 = (moles of CaCl2) / (total moles)

total moles = moles of Cl- ions + moles of Ca2+ ions + moles of water

= 0.44 + 0.22 + 20.83

=21.49

So, mole fraction = 0.44 / (21.49) = 0.02

Guess what !!! density is not used. No need

4 0

3 years ago

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