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Iteru [2.4K]
3 years ago
13

What is the mass of 4.99×1021 platinum atoms?

Chemistry
1 answer:
charle [14.2K]3 years ago
8 0

Answer:

\boxed {\boxed {\sf 1.62 \ g \ Pt}}

Explanation:

We are asked to find the mass of a number of platinum (Pt) atoms.

<h3>1. Convert Atoms to Moles </h3>

First, we convert atoms to moles using Avogadro's Number or 6.022 × 10²³. This is the number of particles (atoms, molecules, formula units, etc.) in 1 mole of a substance. In this case, the particles are platinum atoms.

We will convert using dimensional analysis so we set up a ratio using the information we know (6.022 × 10²³ platinum atoms in 1 mole of platinum).

\frac {6.022 \times 10^{23} \ atoms \ Pt}{ 1 \ mol \ Pt}

We are converting 4.99 ×10²¹ atoms of Pt to moles of Pt, so we multiply by this value.

4.99 \times 10^{21} \ atoms \ Pt *\frac {6.022 \times 10^{23} \ atoms \ Pt}{ 1 \ mol \ Pt}

Flip the ratio so the units of atoms of platinum cancel.

4.99 \times 10^{21} \ atoms \ Pt *\frac { 1 \ mol \ Pt}{6.022 \times 10^{23} \ atoms \ Pt}

4.99 \times 10^{21} *\frac { 1 \ mol \ Pt}{6.022 \times 10^{23}}

\frac { 4.99 \times 10^{21}}{6.022 \times 10^{23}} \ mol \ Pt

Divide.

0.008286283627 \ mol \ Pt

<h3>2. Convert Moles to Grams </h3>

Next, we convert moles to grams using the molar mass. This is the mass of 1 mole of a substance. This is found on the Periodic Table because it is equivalent to the atomic mass, but the units are grams per mole instead of atomic mass units. Look up platinum's molar mass.

  • Pt: 195.08 g/mol

Set up another ratio using this new information (195.08 grams of Pt in 1 mole of Pt).

\frac {195.08 \ g \ Pt}{ 1 \ mol \ Pt}

Multiply by the number of moles we just calculated.

0.008286283627 \ mol \ Pt*\frac {195.08 \ g \ Pt}{ 1 \ mol \ Pt}

The units of moles of platinum cancel.

0.008286283627*\frac {195.08 \ g \ Pt}{ 1 }

0.008286283627* {195.08 \ g \ Pt}

1.61648821\ g \ Pt

<h3>3. Round</h3>

The original measurement of atoms ( 4.99 ×10²¹ ) has 3 significant figures, so our answer must have the same. For the number we found, that is the hundredth place. The 6 in the thousandth place tells us to round the 1 up to a 2.

1.62 \ g \ Pt

There are approximately <u>1.62 grams of platinum</u> in 4.99 ×10²¹ atoms of platinum.

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Element X had a mass of 300g and a 1/2 life of 10 years. how many grams will remain after 40 years?
kiruha [24]
<h3>Answer:</h3>

18.75 grams

<h3>Explanation:</h3>
  • Half-life refers to the time taken by a radioactive material to decay by half of the original mass.
  • In this case, the half-life of element X is 10 years, which means it takes 10 years for a given mass of the element to decay by half of its original mass.
  • To calculate the amount that remained after decay we use;

Remaining mass = Original mass × (1/2)^n, where n is the number of half-lives

Number of half-lives = Time for the decay ÷ Half-life

                                 = 40 years ÷ 10 years

                                  = 4

Therefore;

Remaining mass = 300 g × (1/2)⁴

                            = 300 g × 1/16

                             = 18.75 g

Hence, a mass of 300 g of an element X decays to 18.75 g after 40 years.

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