I just started Chemistry please

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Discussion Overview

The discussion revolves around calculating the density of a sample substance composed of copper, aluminum, and iron, given their mass percentages and individual densities. Participants are exploring methods to derive the density from the provided data, including definitions and interpretations of density and mass percentages.

Discussion Character

  • Homework-related
  • Exploratory
  • Technical explanation

Main Points Raised

  • One participant requests assistance in writing an equation to determine the density of a sample substance with specified mass percentages and densities of its components.
  • Another participant suggests multiplying each percentage by the corresponding density and summing the results, although they acknowledge their lack of chemistry knowledge.
  • Several participants inquire about the definition of density, indicating a need for clarification on the concept before proceeding with the calculations.
  • There is a discussion about what the percentages represent, with clarification that they refer to mass percentages in the context of the sample.
  • A participant proposes a method involving assuming a 100-gram sample to simplify the calculation of individual component masses and their contributions to the overall density.

Areas of Agreement / Disagreement

Participants generally agree on the need to clarify the definition of density and the meaning of mass percentages. However, there are multiple approaches suggested for calculating the density, and no consensus on a single method has been reached.

Contextual Notes

Some participants express uncertainty about the definitions and calculations involved, indicating that assumptions about sample size and the interpretation of density may affect the results. There are also unresolved questions regarding the correct approach to the problem.

rikku
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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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