UNCERTAINTY OF MEASUREMENT

 

         
    Uncertainty of measurement is the doubt that exists about the result of any measurement. You might think that well-made rulers, clocks and thermometers should be trustworthy, and give the right answers. But for every measurement - even the most careful - there is always a margin of doubt. In everyday speech, this might be expressed as ‘give or take’ ... e.g. a stick might be two meters long 'give or take a centimeter'.



Take a look at the difference in measurement readings using these two different rulers.

Using the ruler below, how long is this leaf?


(measurement in centimeters)






Answer: about 3.56 cm

source: https://www.wmo.int/pages/prog/gcos/documents/gruanmanuals/UK_NPL/mgpg11.pdf

FIRE DISTINGUISHERS

I was checking your quiz papers and a handful of you guys answered "FIRE DISTINGUISHER" instead of fire extinguisher. Really?

In case you are still not convinced, here's an illustration of how these fire distinguishers screw things up.

FIRE DISTINGUISHERS are pretty useless. CUTE, but useless.

MEASUREMENT: An Overview

Measurement (from Old French, mesurement) is the assignment of numbers to objects or events. It is a cornerstone of most natural sciences, technology, economics, andquantitative research in other social sciences.

          Any measurement can be judged by the following meta-measurement criteria values: level of measurement (which includes magnitude), dimensions (units), and uncertainty. They enable comparisons to be done between different measurements and reduce confusion. Even in cases of clear qualitative similarity or difference, increased precision through quantitative measurement is often preferred in order to aid in replication.

Measurements are most commonly made in the SI system, which contains seven fundamental units: kilogram, metre, candela, second, ampere, kelvin, and mole. Six of these units are artifact-free (defined without reference to a particular physical object which serves as a standard); the definition of one remaining unit, the kilogram is still embodied in an artifact which rests at the BIPM outside Paris. Eventually, it is hoped that new SI definitions will be uniformly artifact-free.

Base quantity	Base unit	Symbol	Current SI constants
time	second	s	hyperfine splitting in Cesium-133
length	metre	m	speed of light in vacuum, c
mass	kilogram	kg	mass of International Prototype Kilogram (IPK)
electric current	Ampere	A	permeability of free space, permittivity of free space
temperature	Kelvin	K	triple point of water, absolute zero
amount of substance	mole	mol	molar mass of Carbon-12
luminous intensity	candela	cd	luminous efficacy of a 540 THz source

Source: http://en.wikipedia.org/wiki/Measurement

THE BUNSEN BURNER

Get to know more about our friend the Bunsen Burner.

source: http://www.proprofs.com/flashcards/upload/a9689954.jpg

Base: supports the whole bunsen burner

Barrel: where air and gas (fuel) mix

Airports: also known as Air Inlet; allows air to enter into the barrel

Needle valve: also known as Gas Spud; it sprays pressurised gas (fuel) into the barrel

Gas inlet: where gas (fuel) enters

Gas valve: regulates the amount of gas (fuel) flowing into the bunsen burner

Collar (not shown in the diagram) adjusts the opening of the air inlet; regulates the amount of air entering the barrel.

COMMON LABORATORY APPARATUS

Here are some common equipment found in the chemistry lab. Do take note that it's TONGS and not tHongs.

Source: http://www.gwd50.org/cms/lib01/SC01000859/Centricity/Domain/364/lab_equipment.gif

LABORATORY SAFETY SYMBOLS

Welcome Chemistry Pals! 

Year 2014 is going to be a great year for CHEMISTRY. I can feel it. My chemistry senses are tingling. Here are some symbols to warn you of some laboratory risks and hazards. Be safe people.

Chemistry Laboratory Safety Rules:

• Do Not Pipette By Mouth - Ever
  You say, "But it's only water." Even if it is, how clean do you think that glassware really is? Using disposable pipettes? I know lots of people who rinse them and put them back! Learn to use the pipette bulb or automated pipetter. Don't pipette by mouth at home either. Gasoline and kerosene should be obvious, but people get hospitalized or die every year, right? I know someone who used his mouth to start the suction on a waterbed to drain it. Do you know what they put in some waterbed additives? Carbon-14. Mmmm...radiation. He couldn't retch fast enough! The lesson is that even seemingly harmless substances may be dangerous!
  
  
• Read the Chemical Safety Information
  A Material Safety Data Sheet (MSDS) should be available for every chemical you use in lab. Read these and follow the recommendations for safe use and disposal of the material.
  
  
• Dress Appropriately (for chemistry lab, not fashion or the weather)
  No sandals, no clothes you love more than life, no contact lenses, and long pants are preferable to shorts or short skirts. Tie long hair back. Wear safety goggles and a lab coat. Even if you aren't clumsy, someone else in the lab probably is. If you take even a few chemistry courses you will probably see people set themselves on fire, spill acid on themselves, others, or notes, splash themselves in the eye, etc. Don't be the bad example to others, remembered for all time for something stupid!
  
  
• Identify the Safety Equipment
  And know how to use it! Given that some people (possibly you) will need them, know the locations of the fire blanket, extinguishers, eyewash, and shower. Ask for demonstrations! If the eyewash hasn't been used in a while the discoloration of the water is usually sufficient to inspire use of safety glasses.
  
  
• Don't Taste or Sniff Chemicals
  For many chemicals, if you can smell them then you are exposing yourself to a dose that can harm you! If the safety information says that a chemical should only be used inside a fume hood, then don't use it anywhere else. This isn't cooking class - don't taste your experiments!
  
  
• Don't Casually Dispose of Chemicals Down the Drain
  Some chemicals can be washed down the drain, while others require a different method of disposal. If a chemical can go in the sink, be sure to wash it away rather than risk an unexpected reaction between chemical 'leftovers' later.
  
  
• Don't Eat or Drink in Lab
  It's tempting, but oh so dangerous... just don't do it!
  
  
• Don't Play Mad Scientist
  Don't haphazardly mix chemicals! Pay attention to the order in which chemicals are to be added to each other and do not deviate from the instructions. Even chemicals that mix to produce seemingly safe products should be handled carefully. For example, hydrochloric acid and sodium hydroxide will give you salt water, but the reaction could break your glassware or splash the reactants onto you if you aren't careful!
  
  
• Take Data During Lab
  Not after lab, on the assumption that it will be neater. Put data directly in your lab book rather than transcribing from another source (e.g., notebook or lab partner). There are lots of reasons for this, but the practical one is that it is much harder for the data to get lost in your lab book. For some experiments, it may be helpful to take data beforelab. No, I'm not telling you to dry-lab or cheat, but being able to project likely data will help you catch bad lab procedure before you are three hours or so into a project. Know what to expect. You should always read the experiment in advance.

Source: http://chemistry.about.com/od/healthsafety/a/aa080104a.htm

MIXTURES Reviewer 3

Section 15.4 Heterogeneous Mixtures Practice Test

	1.	A suspension is _________.

		a.	a heterogeneous mixture
		b.	a homogeneous mixture
		c.	a solution
		d.	impossible to prepare

	2.	A colloid contains particles that ____________________.

		a.	are smaller than atoms
		b.	are between 1 nm and 1000 nm in diameter
		c.	settle out if left undisturbed
		d.	are atomic-size in scale

	3.	The Tyndall effect describes ______________.

		a.	precipitation of colloidal particles using electrically charged plates
		b.	the adsorption of positive ions onto the surface of a hydrophilic solid
		c.	hydrophobic interactions between nonpolar molecules
		d.	the scattering of light by colloidal particles

	4.	Which one of the following is an example of an emulsion?

		a.	shaving cream
		b.	fog
		c.	mayonnaise
		d.	styrofoam

Answers: a b d c