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2 years ago

Round off 318.90 to 2 significant figures

Chemistry

1 answer:

motikmotik2 years ago

6 0

Answer:

320

Explanation:

Because the question is asking for 2 significant figures, you want to try to get rid of all of the numbers to the right of the 1. That way, the only numbers that will be significant are the numbers in the position of the 3 and the 1.

Before you can make the rest of the numbers equal 0, you need to correctly round the number in the last significant position (the number 1).

If the number to the right of the 1 is from 0-4, the number stays the same. If the number is from 5-9, the 1 needs to be increased by a unit.

Since the number to the right is an 8, you need to change the 1 to a 2. Now, you can make all of the other numbers a 0. There should be no decimal place because it would mean that the zero to the left of it is significant.

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pentagon [3]

Answer:

1. H₂SO₄ + Na₂CO₃ ⇒ Na₂SO₄ + H₂O + CO₂

sulfuric acid + sodium carbonate ⇒ sodium sulfate + water + carbon dioxide

2. 2 HCl + Mg(HCO₃)₂ ⇒ MgCl₂ + 2 H₂O + 2 CO₂

hydrochloric acid + magnesium hydrogencarbonate ⇒ magnesium chloride + water + carbon dioxide

Explanation:

1. Sulfuric acid is H₂SO₄. Sodium carbonate is Na₂CO₃.

H₂SO₄ + Na₂CO₃ ⇒ Na₂SO₄ + H₂O + CO₂

sulfuric acid + sodium carbonate ⇒ sodium sulfate + water + carbon dioxide

2. Hydrochloric acid is HCl. Magnesium hydrogencarbonate is Mg(HCO₃)₂.

2 HCl + Mg(HCO₃)₂ ⇒ MgCl₂ + 2 H₂O + 2 CO₂

hydrochloric acid + magnesium hydrogencarbonate ⇒ magnesium chloride + water + carbon dioxide

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3 years ago

HeLpPp asap I’ll mark you as brainlister

jeka57 [31]

It’s 1 or 3 sorry if this is wrong

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2 years ago

What happens to an object as its thermal energy increases?

aleksandr82 [10.1K]

Answer:

It heats up

Explanation:

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3 years ago

Which of the following types of radiation can be shielded by piece of paper or fabric

Keith_Richards [23]

There are 3 major types of radiation. The Alpha, Beta and Gamma radiation. It is the Alpha radiation that can be stopped by a piece of paper or fabric. Beta on the other hand can be stopped by plastic or a thin sheet of metal and Gamma by a piece of aluminum foil or lead.

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3 years ago

For Na2HPO4:(( (Note that for H3PO4, ka1= 6.9x10-3, ka2 = 6.4x10-8, ka3 = 4.8x10-13 ) a) The active anion is H2PO4- b) The activ

Komok [63]

Answer:

Check the explanation

Explanation:

Answer – Given, $H_3PO_4$ acid and there are three Ka values

$K_{a1}=6.9x10^8, K_{a2} = 6.2X10^8, and K_{a3}=4.8X10^{13}$

The transformation of $H_2PO_4- (aq) to HPO_4^2-(aq)$ is the second dissociation, so we need to use the Ka2 = 6.2x10-8 in the Henderson-Hasselbalch equation.

Mass of KH2PO4 = 22.0 g , mass of Na2HPO4 = 32.0 g , volume = 1.00 L

First we need to calculate moles of each

Moles of KH2PO4 = 22.0 g / 136.08 g.mol-1

= 0.162 moles

Moles of Na2HPO4 = 32.0 g /141.96 g.mol-1

= 0.225 moles

[H2PO4-] = 0.162 moles / 1.00 L = 0.162 M

[HPO42-] = 0.225 moles / 1.00 L = 0.225 M

Now we need to calculate the pKa2

pKa2 = -log Ka

= -log 6.2x10-8

= 7.21

We know Henderson-Hasselbalch equation

pH = pKa + log [conjugate base] / [acid]

pH = 7.21 + log 0.225 / 0.162

= 7.35

The pH of a buffer solution obtained by dissolving 22.0 g of KH2PO4 and 32.0 g of Na2HPO4 in water and then diluting to 1.00 L is 7.35

6 0

3 years ago