Some Basic Concepts of Chemistry Test

Result

Some Basic Concepts of Chemistry Test - 41

Score
-
out of -
Rank
-
out of -

TIME Taken - -

SHARING IS CARING

If our Website helped you a little, then kindly spread our voice using Social Networks. Spread our word to your readers, friends, teachers, students & all those close ones who deserve to know what you know now.

Weekly Quiz Competition

Question 1
1 / -0

$$2K(s)+2{H}_{2}O(l)\rightarrow 2KOH(aq)+{H}_{2}(g)$$
If $$3.0$$ moles of potassium react with excess water, what volume of hydrogen gas will be produced?

A
$$1.5L$$

B
$$22.4L$$

C
$$67.2L$$

D
$$33.6L$$

Solution

Given, $$2K(s) + 2H_2O(l) \rightarrow 2KOH(aq) + H_2 (g)$$
$$2\space moles$$ of Potassium on reaction gives $$1 \space mole$$ of Hydrogen [ 22.4 at STP]
$$2\space moles$$ of $$K \rightarrow 22.4 \space Litres $$ of $$H_2$$
$$2\space moles$$ of $$K = \dfrac{3\times 22.4}{2} = 33.6 \space Litres$$ of $$H_2$$
So, $$33.6\space Litres$$ of Hydrogen are produced.
Question 2
1 / -0

Use the figure below to answer the question that follows.
Which of the four molecules has the highest percentage of nitrogen, by mass?

A
I

B
II

C
III

D
IV

Solution

If the other atoms of molecules have comparitively less atomic mass then percentage of central atom is more.
In $$II \Rightarrow N_2H_4$$ has Hydrogen atoms which has very less atomic mass (1) compared to Nitrogen (14). So, $$N_2H_4$$ has highest percentage of Nitrogen.
Question 3
1 / -0

A $$5.0g$$ sample of copper(II) oxide containing an inert contaminant is analyzed and found to contain $$3.0g\ Cu$$. Using molar masses of $$64g/mol$$ for copper, and $$16g/mol$$ for oxygen, determine the percent purity of the copper(II) oxide sample.

A
$$80$$%

B
$$75$$%

C
$$60$$%

D
$$50$$%

Solution

Given, Mass of $$CuO$$ sample $$= 5\space g$$
Mass of $$Cu$$ found $$= 3\space g = \dfrac{3}{64} \space moles$$ of Copper
So, $$\dfrac{3}{64} \space moles $$ of $$CuO$$ must be present
Mass of $$\dfrac{3}{64} \space moles $$ of $$CuO = \dfrac{3}{64} [64 + 16] = 3.75 \space g$$
So, percentage of Purity$$= \dfrac{3.75}{5} \times 100 = 75\%$$
Question 4
1 / -0

A student would like to use gravimetric analysis to determine the percent by mass of magnesium chloride in a contaminated mixture containing magnesium chloride.
Which of the following compounds would be the BEST substance to react the contaminated mixture with to determine the mass percent?

A
silver nitrate.

B
Potassium chloride.

C
Sodium acetate.

D
Lithium sulfate.

Solution

The student needs to form a precipitate that they can weigh to determine the amount of magnesium or chlorine in the contaminated sample. Knowledge of the solubility rules is necessary for this question. Group 1 elements, nitrates, and acetates always form soluble compounds. Halogens are usually soluble except with silver, lead and mercury. Silver nitrate will be the only substance to form a precipitate. Magnesium chloride and silver nitrate will react to form a silver chloride precipitate.
Question 5
1 / -0

A hydrate sample of magnesium chloride is analyzed and found to contain $$53.18$$% water.
How many water molecules are found in the formula for this hydrate?

A
Two

B
Four

C
Six

D
Eight

Solution

$$\begin{array}{l}\text { Let, the hydrated sample contains } x \text { molecules of } \mathrm{H}_{2} \mathrm{O} \text { . } \\\text { so, given sample becomes } \mathrm{MgCl}_{2} \cdot x\mathrm{H}_{2}\mathrm{O} \text { . } \\\text { Now, it is given that } 53.18 \% \text { of the formula is } \mathrm{H}_{2} \mathrm{O} \text { . }\end{array}$$

$$\begin{array}{l}\text { Thus, } \dfrac{x \times 18}{(18x+95)}=\dfrac{53.18}{100 .} \Rightarrow x=6 \\\text { Hence, there are six water molecules are found in this hydrate. }\end{array}$$
Question 6
1 / -0

What is the correct unit for the following solution?

$$10.5\ g$$ of $${C}_{7}{H}_{8}O$$ in $$100\ g$$ of water as a topical treatment for poison ivy.

A
$$w/w$$

B
$$m$$

C
$$M$$

D
$$v/v$$

Solution

When a given amount of solute in gram is dissolved in a given amount of solvent in gram, then the solution formed is expressed in the form of w/w unit.

Hence, option A is correct.
Question 7
1 / -0

What would be the approximate weight of $$1.204\times 10^{24}$$ bromine atoms?

A
80 grams

B
120 grams

C
160 grams

D
180 grams

E
200 grams

Solution

The atomic weight of bromine is 80.
So, 80-gram bromine contains Na atoms.
So, $$1.204\times10^{24}$$ bromine atoms will weigh: $$80\div 6.02\times10^{23}\times 1.204\times10^{24}=160\ gram$$
Question 8
1 / -0

If a copper-containing compound contains $$4.999$$% $$Cu$$ by mass and there are $$2$$ copper atoms per formula unit, what is the molar mass of the compound?

A
$$2547\ g/mol$$

B
$$47.50\ g/mol$$

C
$$31.75\ g/mol$$

D
$$1274\ g/mol$$

Solution

Let molar mass of compound $$= M$$
In $$1\space mole$$ of compound there are two Copper atoms i.e. $$128\space gms$$ of Copper.
Given, $$4.999\%$$ ofCopper by mass
So, $$(\% \text{ of Copper}) \times \text{Molar mass} = \text{Mass of Copper} $$
$$\Rightarrow (\dfrac{4.999}{100}) \times M = 128 \space gms$$
$$\Rightarrow M = \dfrac{12800}{4.99} = 2547 \space g/mol$$
Question 9
1 / -0

Which pair of substances share the same mass percent of each element?

A
$$NaOCl$$ and $$OCl^{-}$$

B
$$CO$$ and $$CO_{2}$$

C
$$C_{6}H_{12}O_{6}$$ and $$C_{3}H_{6}O_{3}$$

D
None of these pairs of substances share the same mass percent.

Solution

When the ratio of number of atoms in a molecule are same then the percentage of each element will be same.
Here, In $$C_6H_{12}O_6$$
$$C:H:O = 6:12:6 = 1:2:1$$
In $$C_3H_{6}O_3$$
$$C:H:O = 3:6:3 = 1:2:1$$
So, $$C_6H_{12}O_6$$ and $$C_3H_{6}O_3$$ has same percent of element.
Question 10
1 / -0

How many atoms of hydrogen are present in $$7.8\ g$$ of $$Al{(OH)}_{3}$$?

A
$$6.0\times {10}^{22}$$

B
$$1.8\times {10}^{23}$$

C
$$1.7\times {10}^{23}$$

D
$$5.1\times {10}^{22}$$

Solution

Molar mass of $$Al(OH)_3 = 27 + 3\times 16 + 3\times 1 = 78\space g$$
So, no. of moles of $$Al(OH)_3 = \dfrac{7.8}{78} = 0.1\space moles$$
$$1\space mole$$ of $$Al(OH)_3$$ has $$6.023 \times 10^{23}$$ atoms.
So, $$0.1\space moles$$ has $$6.023 \times 10^{22}$$ atoms.

User

Question Analysis

Correct -
Wrong -
Skipped -

My Perfomance

Score
-
out of -
Rank
-
out of -

Re-Attempt Weekly Quiz Competition

Some Basic Concepts of Chemistry Test - 41

Result

Some Basic Concepts of Chemistry Test - 41

Score

-

Rank

-

SHARING IS CARING

Question 1

$$1.5L$$

$$22.4L$$

$$67.2L$$

$$33.6L$$

Solution

Question 2

I

II

III

IV

Solution

Question 3

$$80$$%

$$75$$%

$$60$$%

$$50$$%

Solution

Question 4

silver nitrate.

Potassium chloride.

Sodium acetate.

Lithium sulfate.

Solution

Question 5

Two

Four

Six

Eight

Solution

Question 6

$$w/w$$

$$m$$

$$M$$

$$v/v$$

Solution

Question 7

80 grams

120 grams

160 grams

180 grams

200 grams

Solution

Question 8

$$2547\ g/mol$$

$$47.50\ g/mol$$

$$31.75\ g/mol$$

$$1274\ g/mol$$

Solution

Question 9

$$NaOCl$$ and $$OCl^{-}$$

$$CO$$ and $$CO_{2}$$

$$C_{6}H_{12}O_{6}$$ and $$C_{3}H_{6}O_{3}$$

None of these pairs of substances share the same mass percent.

Solution

Question 10

$$6.0\times {10}^{22}$$

$$1.8\times {10}^{23}$$

$$1.7\times {10}^{23}$$

$$5.1\times {10}^{22}$$

Solution

User

Question Analysis

My Perfomance

Score

-

Rank

-

Results Announcement on: coming Monday

Stay Tuned: We’ll update you on your result via email or SMS.