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Physical Science

Conservation of Mass in 5th grade

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Elizabeth Manning 870 Points

Hi colleagues, I am struggling with conservation of mass labs in 5th grade due to lack of accuracy on their part in measuring. I have tried a chemical reaction before and after, with a balloon over the flask, and also ice melting in a baggie before and after. In both cases, the students are not able to accurately measure on the triple beam balance, so they get different before and afters.  Has anyone else had this problem? Would digital balances be more accurate? My students have a lot of practice with the balances and the seem to do great with relative mass, i.e. figuring out which is heavier, but when it comes to accuracy, they are definitely off.

Pamela Dupre 92369 Points

I agree, this concept is a struggle. In regards to digital balances, I would go with those. I meet with a team of middle and high school science teachers and when this question came up, they said they don't even use triple beam balances! In elementary we still do because students have to know those particular tools.

John Hoayun 405 Points

Hello, I have minimized the usage of the triple beam balance. Instead I use the digital scales. They work real well.

Cristina Toj 835 Points

Digital scales are definitely something to think of using. This way there is less room for human error.

Pamela Dupre 92369 Points

I've taught elementary students how to use triple beam balance scales for years. I was surprised last year when a middle school and a high school teacher both told me they don't even use them anymore! So now, I teach using the digital scales in addition to the triple beam balance scales.

Daniel Carroll 18610 Points

A human can make an error reading a digital balance just as easily as a triple beam balance. You should try it yourself a few times just to see what the approximate range should be for the measurements. You are expecting all of the numbers to add up? Maybe there are other losses of mass that aren't considered. Are the masses too small to be measuring on a triple beam balance? Electronic balances are nice, but they will need to be careful about them for the following reasons. [ol]

• be sure the scaled is zeroed (tared)
• understand what units you are measuring
• will you tare it with the containers or without the containers
• If the scales are very sensitive they will be very sensitive...
• [/ol] Then.. I don't talk about 'error'. If you made errors... do it over. There are factors that may influence the outcome. For example: maybe some of the gas slipped out of the balloon when you took it off. Not an error, but an explainable loss of mass.

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