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2 years ago

How many moles are present in 45.0 g of lithium oxide (Li2O)?

1 answer:

4 0

Molar mass Li2O = 7.0 x 2 + 16 => 30 g/mol

1 mole Li2O ---------- 30 g
( moles Li2O ) -------- 45.0 g

moles Li2O = 45.0 x 1 / 30

moles Li2O = 45.0 / 30

= 1.50 moles of Li2O

hope this helps!

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What is the Ka of a weak acid (HA) if the initial concentration of weak acid is 4.5 x 10-4 M and the pH is 6.87? (pick one)

rewona [7]

Answer:

Ka = $4.04 \times 10^{-11}$

Explanation:

Initial concentration of weak acid = $4.5 \times 10^{-4}\ M$

pH = 6.87

$pH = -log[H^+]$

$[H^+]=10^{-pH}$

$[H^+]=10^{-6.87}=1.35 \times 10^{-7}\ M$

HA dissociated as:

$HA \leftrightharpoons H^+ + A^{-}$

(0.00045 - x) x x

[HA] at equilibrium = (0.00045 - x) M

x = $1.35 \times 10^{-7}\ M$

$Ka = \frac{[H^+][A^{-}]}{[HA]}$

$Ka = \frac{(1.35 \times 10^{-7})^2}{0.00045 - 0.000000135}$

0.000000135 <<< 0.00045

$Therefore, Ka = \frac{(1.35 \times 10^{-7})^2}{0.00045 } = 4.04 \times 10^{-11}$

5 0

2 years ago

Which veriable should he change, measure and control (temp of water, volume of water and mass of sodium chloride that dissolve )

erma4kov [3.2K]

I would say
change: Temp
Measure: Mass
Control: Volume

7 0

2 years ago

6 NaOH + 2 Al ???? 2 Na3AlO3 + 3 H2 How much aluminum is required to produce 17.5 grams of hydrogen? How many moles of NaOH are

ANTONII [103]

Answer:

a) 157.5 grams of aluminum.

b) 1 mol

c) 9 g

Explanation:

The reaction is :

$6 NaOH + 2Al ---> 2 Na_{3}AlO_{3} + 3H_{2}$

As per balanced equation

a) 3 moles of hydrogen will be produced from two moles of aluminium.

The atomic mass of aluminium = 27

therefore

3X2 grams of hydrogen is produced from 2 X 27 grams of Al

1 gram of hydrogen will be produced from $\frac{2X27}{3X2}= 9$ g

therefore 17.5 will be produced from = 9X 17.5 = 157.5 grams of aluminum.

b) as per balanced equation three moles or six gram of hydrogen is produced from 6 moles of NaOH.

Therefore 1 g of hydrogen will be produced from = $\frac{6}{6}$

or 1 gram will be prepared from = 1 mole

c) from balanced equation three moles are produced from two moles of Al (27X2 = 54 g).

thus from 54 grams gives 6 grams of hydrogen

1 grams will give = $\frac{54X1}{6}= 9 g$

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2 years ago

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