Questions and Answers

Your Questions About X10

May 24, 2013

Thomas asks…

How would i find the amount of Significant numbers in Scientific notation?

so im suposed to identify the amount of SF . ive got 2 questions where it has scientific notation.
it is : 7.0×10^3 and 4.0 x10^-4

would i convert them to standard numbers or the numbers before the “x” is the number i calculate the amount of SF?

Administrator answers:

No … Don’t write them in standard form b/c you’ll just be writing a heap of insignificant zeros and you won’t know if any of the zeros should be included as significant

When numbers are written in scientific notation it’s really easy to get the number of sig figs b/c all the insignificant zeros are missing …

The number of sig figs is equal to the number of digits (including any zeros) that are written b4 the times sign

so 7.0 x 10³ has 2 sig figs

4.0 x 10^(-4) also has 2 sig figs

btw … The best way to write numbers so that the number of sig figs is real clear is to use scientific notation … Never any doubt if a zero is significant or not … All the digits b4 the “x” are significant

John asks…

What combination of substances will give a buffered solution that has a pH of about 8?

Explain the reason for your choice. NH3 mixed with NH4Cl (Kb for NH3 = 1.8 x10–5) or C5H5N mixed with C5H5NHCl (Kb for C5H5N = 1.7×10–9)

Administrator answers:

PKb of NH3 = 4.7
pKb of C5H5NHCl =8.8

pOH = 14 – 8 = 6

6 = 4.7 + log [NH4+]/ [NH3]
[NH4+]/ [NH3] = 20

6 = 8.8 + log [C5H5NH+]/[C5H5N]
[C5H5NH+]/ [C5H5N]= 0.0016 => your answer

the ratio between NH4+ and NH3 is too big

Jenny asks…

how to clean the sticky residue left from a rug pad?

We have laminate floors and when we bought the area rug (8′x10‘) the salesman said we needed a pad and sold us a thin sticky one. I moved the rug and pad and there is a sticky residue on the floor that I can’t get off. Being laminate I don’t want to ruin the floor trying to clean it. Can you offer any suggestions?

Administrator answers:

Is this a laminate linoleum or laminate wood flooring?

If it’s laminate linoleum you can use rubbing alcohol.
If it’s laminate wood flooring try using Murphy’s oil soap.

Ken asks…

What are some good gift ideas for a person in an Assisted Living facility?

It’s very different than a nursing home. My person is pretty active and likes to play games, read, and collects University of Texas stuff. However, her room is only 10′x10‘, so space is limited.

Administrator answers:

Hmm- Well, you could try books.

Or- hey, maybe you can find some blankets, towels, or throws with the University of Texas logo on it!

William asks…

Can the error bars change magnitude between various points in a single series of data?

In other words, lets say you have a series of data points (x1, x2, x3, ….. x10). And this data as a whole has particular standard deviation (s) and mean (x_bar). My assumption is that if you were to use standard error as the basis of the error bars, the error bars would all have to have equal magnitudes. But, I have seen some data where these error bars changed magnitude between different points in the data, how is this possible?

Administrator answers:

” My assumption is that if you were to use standard error as the basis of the error bars, the error bars would all have to have equal magnitudes. ” Wrong!

When you estimate S(x), you work with the “average” of the quadratic deviations from the mean.

Paul asks…

What’s the best projector under $1500 that you can get for a large partialy lit room?

The room is probably 25′x45′ with the screen coming doing infront of a stage area. We would like to move the projector around to other rooms as well but it would do most of it’s work here. Some still PP slides and some video. The screen is about 10′X10‘ and would be about 25′ from the projector.

Administrator answers:

You will probably have to trade off somewhere. I did a search on available projectors, assuming 2000 lumen brightness minimum (to address light in the room) and a throw distance of 25′ onto a 150″ screen. See the link for results — the least expensive was about $2300. You can redo the search with different parameters.

This site also has good reviews, additional info andrecommendations (including lists of popular projectors by application).

Hope this helps.

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