I just started Chemistry please

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To determine the density of a sample substance composed of 15% copper, 35% aluminum, and 50% iron by mass, the discussion emphasizes understanding the definition of density as mass per unit volume. The participants suggest starting with a hypothetical 100-gram sample to simplify calculations, where the mass contributions would be 15 grams of copper, 35 grams of aluminum, and 50 grams of iron. The approach involves calculating the volume of each component using their respective densities (copper at 8.92 g/cm³, aluminum at 2.70 g/cm³, and iron at 7.86 g/cm³) through dimensional analysis. After determining the individual volumes, the total volume is summed, and the overall density of the sample is found by dividing the total mass (100 grams) by this total volume. This method provides a clear pathway to solving the problem while reinforcing the fundamental concepts of mass and density in chemistry.
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I just started Chemistry need help please!

Help me write equation for the following problem :smile:
A sample substance is 15% copper, 35% aluminum, 50% iron by mass. Density of copper = 8.92, aluminum=2.70, iron=7.86. What is the density of the sample? :approve:
I have some ideas but want to check.
 
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I'm guessing, I haven't taken Chemistry yet: Multiply each percentage by the density of the substance. For example 0.35 x 8.9 - then add all your resultant numbers.
 
How is density defined?
 
so-crates said:
How is density defined?
what do you mean?
 
what do % represent here? Mass?
 
rikku said:
what do you mean?

I mean, what is the definition of density? That might be a good place to start and might give you some insight into the problem. I am trying to follow the method of my namesake: The answer to the question is already in your mind, it just needs to be discovered. :smile:
 
rikku said:
what do % represent here? Mass?

Yes. When it says 50% by mass, it means that in a 10g sample, 5g of the mass is iron.

I like the way you think, so-crates.
 
Help me write equation for the following problem
A sample substance is 15% copper, 35% aluminum, 50% iron by mass. Density of copper = 8.92, aluminum=2.70, iron=7.86. What is the density of the sample?
I have some ideas but want to check.

assume you have a 100 gram sample so you would have 15 grams of copper 35 of al and 50 grams of Fe, now density is mass over volume so 8.92 g/cm^3 so do dimensional analysis and see how much of the 100 grams the aluminum takes up, then add that for each value so you should get what all of them take up individually so then you get the 100 grams you assumed you had, and divide by the added values that you got
 

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