Learn the toughest concepts covered in your GOB - General, Organic, and Biological Chemistry class with step-by-step video tutorials and practice problems.

Matter and Measurements

From the simplest view, **Specific Gravity** represents density without the units.

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Specific Gravity

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Now, if you've heard about density, you might have heard about specific gravity. Now, specific gravity represents the density of a substance divided by the dead sea of water at the same temperature. Now we're gonna say, since the units cancel out when it comes to specific gravity, we're going to say that it is unit lous. So specific gravity has no units involved. We're gonna say note as the temperature changes, the density of water changes. So if we take a look here, we have the specific gravity of water. And again, that's density of a substance in grams per minute. Leader, if we're assuming it's in uh liquid or solid form divided by the density of water, The units would cancel out. And that's why specific gravity is you nicolas. Now we just said that as a temperature changes, the density of water changes. We tend to hear that the density of water is 1.0 g per familiar. That is not exactly true. That's only true when the temperature is exactly 3.98°C. If the temperature to change, the density of water slightly changes, we can see here the density of water at negative 30 degrees Celsius, zero degrees Celsius, 10 degrees Celsius, 25 degrees Celsius and 100 degrees Celsius. We see that the density is slightly changing as we increase the temperature, and we can see that the general trend is that it is decreasing as we go higher and higher in terms of temperature. All right, so just remember specific gravity is the density of a substance divided by the density of water. Units cancel out means that specific gravity has no units. Yeah.

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Specific Gravity Example 1

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here, we're told that if the specific gravity of sulfuric acid is 1.27 at room temperature, which is 25 degrees Celsius, what is its mass in milligrams for 2.3 liters. Alright, so, remember, specific gravity equals the density of the substance, which is sulfuric acid. Okay, divided by the density of water. So let's fill in the party. They're telling us. They tell us that the specific gravity of sulfuric acid is 1. With the temperature, we can look at the chart and see what is the density of water at 25 degrees Celsius. That would be 250. g per millimeter. And here this will be our X. We don't know what the density of sulfuric acid is. All right, So we're going to do first is we're gonna cross multiply these two together. So 1.27 times the density of water at 25 degrees Celsius. When we do that, that's going to give me X equals 1.26619 g per millimeter. Okay, that's gonna be grams per one million. Er Now they're giving us 23 leaders Here. If we convert that two, that comes out to 2300. And what we need to realize here is that now if I bring in the 2300 ml, here. They will cancel out with the middle leaders from the density we isolated and that will give me the mass of sulfuric acid at this point. Which would come out to (291) 2.237g. But remember they're not asking for the answer, ingram's who wanted in milligrams? So we have to do one more conversion grams. Go on the bottom milligrams go on top. Remember millie, the metric prefix gets one so one millie is 10 to the negative. Three miller on grams, cancel out. And now we're gonna have milligrams as our answer, which is going to come out to 2.9 times 10 to the six mg. We converted into scientific notation. Here we have. Our answer is 2.9 which has two sig figs because 2.3 has to sig figs. This has 36 figs. This has to sig figs. Remember we go with the least number of sig figs. So again, our answer here would be 2.9 times 10 to the six mg for sulfuric acid.

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Problem

What is the specific gravity of lithium metal (in g/mL) at 10.0ºC if a cube measures 0.82 cm x 1.45 cm x 1.25 cm and has a mass of 0.794 g?

A

0.55

B

0.504

C

0.53

D

1.87

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Problem

Ethyl alcohol has a specific gravity of 0.7892 at 10ºC. What is the volume of 250 g of ethyl alcohol?

A

317 mL

B

197 mL

C

320 mL

D

371 mL

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